Method for treating wastewater generated during synthesis of bisphenol A epoxy resin

Abstract

The invention belongs to the technical field of wastewater treatment, and discloses a method for treating wastewater generated by synthesizing bisphenol A epoxy resin, which comprises the following steps: adjusting the pH value of the wastewater generated by synthesizing bisphenol A epoxy resin to 1-5, mixing the wastewater with a catalyst and oxygen to obtain first wastewater, and setting the addition amount of the oxygen as follows: the oxygen content is 1.02-1.2 times of the COD (Chemical Oxygen Demand) of the wastewater. The temperature and pressure of the first wastewater are adjusted, and the first wastewater is subjected to a subcritical water catalytic oxidation reaction until second wastewater with TOC smaller than or equal to 150 mg / L is obtained. And adjusting the temperature of the second wastewater to 50-60 DEG C and the pressure to standard atmospheric pressure to obtain third wastewater. And removing the catalyst in the third wastewater to obtain fourth wastewater. The fourth wastewater is subjected to adsorption treatment until a sodium chloride solution with TOC smaller than or equal to 10 mg / L is obtained. The method can avoid supersaturated precipitation of sodium chloride, and reduces the requirements on temperature, pressure and other conditions in the catalytic oxidation process, thereby reducing the control difficulty and improving the stability of the reaction process.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology. More specifically, this invention relates to a method for treating wastewater generated from the synthesis of bisphenol A type epoxy resin. Background Technology

[0002] One synthetic route for bisphenol A type epoxy resin is as follows: using bisphenol A, epichlorohydrin, liquid alkali, toluene, and polyethylene glycol as raw materials, epichlorohydrin and bisphenol A undergo etherification and ring-closure reactions under alkaline conditions. After the reaction is complete, the crude resin is sent to a refining reactor for refining. During the refining process, nearly saturated sodium chloride wastewater is generated, containing 20-26% sodium chloride, 0.5-1% crude glycerol, 5000 mg / L organic polymers, 100 mg / L toluene, 350 mg / L total nitrogen, 150 mg / L ammonia nitrogen, and a COD value of 8000-12000 mg / L. If this wastewater is directly evaporated and concentrated, the resulting sodium chloride will contain organic matter, making it difficult to reuse.

[0003] Patent application No. 202211456317.7 discloses a method for treating epichlorohydrin and epoxy resin wastewater and its application, employing a two-step catalytic wet oxidation method to improve the removal efficiency of organic matter. However, this method also has drawbacks: First, to improve the removal rate of organic matter, the method has stringent requirements for reaction conditions and equipment; second, after wet oxidation treatment, the cooling and depressurization process of the oxidation liquid will generate a large amount of water vapor that will be released with the gas, and when the sodium chloride content is high, it will cause sodium chloride to precipitate and clog the equipment; third, the secondary wet oxidation method is not ideal for removing small molecule organic matter.

[0004] In view of this, there is an urgent need to provide a method for treating wastewater generated during the synthesis of bisphenol A type epoxy resin, which can reduce sodium chloride precipitation during the treatment process, lower the requirements for reaction conditions, improve the removal rate of organic matter, and improve the stability of effluent quality. Summary of the Invention

[0005] To address at least one or more of the technical problems mentioned above, embodiments of the present invention provide a method for treating wastewater generated from the synthesis of bisphenol A type epoxy resin, comprising: a first step of adjusting the pH of the wastewater from the synthesis of bisphenol A type epoxy resin to 1-5, mixing it with a catalyst and oxygen to obtain a first wastewater, wherein the amount of oxygen added is set to be 1.02-1.2 times the COD of the wastewater; a second step of adjusting the temperature and pressure of the first wastewater to allow it to undergo a subcritical water catalytic oxidation reaction until a second wastewater with TOC ≤ 150 mg / L is obtained; a third step of adjusting the temperature of the second wastewater to 50°C-60°C and the pressure to standard atmospheric pressure to obtain a third wastewater; a fourth step of removing the catalyst from the third wastewater to obtain a fourth wastewater; and a fifth step of subjecting the fourth wastewater to adsorption treatment until a sodium chloride solution with TOC ≤ 10 mg / L is obtained.

[0006] According to one embodiment of the present invention, the heat from the second wastewater in the third step is used to preheat the first wastewater in the second step.

[0007] According to one embodiment of the present invention, in the first step, the catalyst is selected from one or more of CuCl2, CeCl3, FeCl3, MoCl5, CoCl2, NiCl2 and ZnCl2, and the amount of catalyst is 0.1%-1% of the mass of wastewater.

[0008] According to one embodiment of the present invention, in the second step, the temperature and pressure of the first wastewater are adjusted to maintain the first wastewater in a liquid state. Preferably, the temperature and pressure of the first wastewater are adjusted to a temperature range of 220°C to 290°C and a pressure range of 5 to 10 MPa.

[0009] According to one embodiment of the present invention, in the second step, the concentration of the second wastewater is controlled to be 80 mg / L ≤ TOC ≤ 100 mg / L.

[0010] According to one embodiment of the present invention, in the fourth step, the catalyst is removed by means of: adjusting the pH of the third wastewater to above 9 using NaOH solution, filtering or centrifuging to recover the catalyst; or, using a chelating resin to recover the catalyst.

[0011] According to one embodiment of the present invention, in the fifth step, the fourth wastewater is treated by adsorption using a salt-resistant adsorption resin.

[0012] According to one embodiment of the present invention, in the first step, 36%~38%wt of concentrated hydrochloric acid is added to adjust the pH.

[0013] The present invention, through the wastewater treatment method provided above for the synthesis of bisphenol A type epoxy resin, uses pure oxygen as an oxidant and strictly controls the amount of oxygen, limiting the excess oxygen to within 1.2 times the standard amount, thereby reducing the amount of gas evaporated during the subcritical water catalytic oxidation process and preventing sodium chloride supersaturation precipitation. By setting the cooling temperature of the second wastewater between 50 and 60°C, a high solubility of sodium chloride can be maintained, further preventing sodium chloride saturation precipitation. The second wastewater with TOC ≤ 150 mg / L obtained through subcritical water catalytic oxidation reduces the requirements for temperature, pressure, and other conditions in the catalytic oxidation process, reducing control difficulty and improving the stability of the reaction process. The lower temperature further reduces the amount of gas evaporation during the oxidation process. By connecting an adsorption treatment after the catalytic oxidation step, residual or difficult-to-remove trace amounts of organic matter from the catalytic oxidation process can be further removed, thereby rapidly and stably obtaining a sodium chloride solution with TOC ≤ 10 mg / L. Furthermore, in some embodiments, by recovering the heat from the catalytic oxidation process output for preheating the feed to the catalytic oxidation process, energy consumption can be reduced. Furthermore, in some embodiments, by setting the second wastewater to 80≤TOC≤100mg / L, the control conditions for catalytic oxidation can be reduced on the one hand, and the amount of organic matter to be treated in subsequent adsorption treatment can be reduced on the other hand. Attached Figure Description

[0014] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent upon reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the invention are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding parts, wherein:

[0015] Figure 1 A schematic diagram illustrating the steps of a method for treating wastewater generated during the synthesis of bisphenol A type epoxy resin is shown. Detailed Implementation

[0016] 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, not all, of the embodiments of the present invention. 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.

[0017] It should be understood that the terms "comprising" and "including" as used in the specification and claims of this invention indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0018] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0019] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] Figure 1 A schematic diagram illustrating the steps of a method for treating wastewater generated during the synthesis of bisphenol A type epoxy resin is shown.

[0021] like Figure 1 The method for treating wastewater generated from the synthesis of bisphenol A type epoxy resin, as shown, includes: a first step S1, adjusting the pH of the wastewater to 1-5, mixing it with a catalyst and oxygen to obtain a first wastewater, wherein the amount of oxygen added is set to be 1.02-1.2 times the COD of the wastewater; a second step S2, adjusting the temperature and pressure of the first wastewater to allow it to undergo a subcritical water catalytic oxidation reaction until a second wastewater with TOC ≤ 150 mg / L is obtained; a third step S3, adjusting the temperature of the second wastewater to 50℃-60℃ and the pressure to standard atmospheric pressure to obtain a third wastewater; a fourth step S4, removing the catalyst from the third wastewater to obtain a fourth wastewater; and a fifth step S5, subjecting the fourth wastewater to adsorption treatment until a sodium chloride solution with TOC ≤ 10 mg / L is obtained.

[0022] The wastewater generated from the synthesis of bisphenol A type epoxy resin mainly includes: sodium chloride content of 20-26%, crude glycerol content of 0.5-1%, organic polymer content of 5000 mg / L, toluene content of 100 mg / L, total nitrogen content of 350 mg / L, ammonia nitrogen content of 150 mg / L, and COD value of 8000-12000 mg / L.

[0023] In the first step S1, the pH of the wastewater is adjusted to 1-5 by adding 36%~38%wt concentrated hydrochloric acid to the equalization tank, creating an acidic environment to prevent catalyst precipitation. The catalyst is then added to the pH-adjusted wastewater, mixed thoroughly, and transported with oxygen through pipelines; this constitutes the first wastewater.

[0024] The catalyst is selected from one or more of CuCl2, CeCl3, FeCl3, MoCl5, CoCl2, NiCl2, and ZnCl2, and the amount of catalyst is 0.1% to 1% of the wastewater mass. The catalysts selected in this invention all have the characteristic of precipitation under alkaline conditions, which facilitates catalyst recovery.

[0025] The amount of oxygen added is set to be 1.02 to 1.2 times the COD of the wastewater. In this invention, by setting a lower limit for the oxygen content, rapid completion of oxidation can be ensured; by setting an upper limit for the oxygen content, the amount of gas evaporation after the subcritical water catalytic oxidation reaction can be reduced, thus preventing the precipitation of sodium chloride from the wastewater. This is because a gas-liquid separation step follows the subcritical water catalytic oxidation; the greater the amount of evaporated gas, the more water vapor it carries. In this invention, the sodium chloride concentration of the raw material is relatively high, and the water vapor carried by the evaporated gas further increases the concentration of sodium chloride in the liquid phase, even leading to saturation and precipitation.

[0026] In the second step S2, adjusting the temperature of the first wastewater can be done in two steps: preheating and supplementary heating. First, preheating is performed using heat generated within the wastewater treatment system. If preheating is insufficient to reach the triggering conditions for subcritical water catalytic oxidation, an external heat source can be used for supplementary heating until the triggering temperature for subcritical water catalytic oxidation is reached. Simultaneously, regarding pressure control, the wastewater is kept in a liquid state throughout the temperature rise process.

[0027] Subcritical water catalytic oxidation is a concept corresponding to supercritical water catalytic oxidation. Supercritical water oxidation (SCWO) refers to the process where, when a fluid in vapor-liquid equilibrium is heated and pressurized, thermal expansion causes a decrease in liquid density, while the increase in pressure causes the vapor-liquid interface to disappear, resulting in a homogeneous system—this is the critical point. When the temperature and pressure of the fluid exceed the critical temperature and critical pressure, respectively, it is said to be in a supercritical state. Supercritical water is an excellent solvent for both organic matter and oxygen; the oxidation of organic matter can proceed in an oxygen-rich homogeneous phase, and the reaction is not limited by the need for phase transition.

[0028] Subcritical water catalytic oxidation refers to adjusting reaction conditions such as temperature and pressure to a level slightly below the critical point of water. Since it is close to the critical point of water, the properties of subcritical water, which are similar to those of nonpolar organic compounds, can be utilized. At the same time, the requirements for reaction conditions are significantly reduced compared to those for supercritical water catalytic oxidation.

[0029] In subcritical water catalytic oxidation, in order to oxidize all or most of the organic matter in the wastewater in one step, the conditions for setting temperature, pressure and other conditions are still quite stringent, and the requirements for the corrosion resistance and pressure resistance of the equipment are also high.

[0030] Further improvements have been made in this invention. When performing subcritical water catalytic oxidation, the requirements for temperature and pressure are further reduced, as long as the generated second wastewater has a TOC ≤ 150 mg / L. Based on this, this invention allows for the setting of lower temperature and pressure parameter combinations, which reduces the difficulty of controlling the reaction conditions, facilitates the stable control of the reaction, and also reduces the requirements for the corrosion resistance and pressure resistance of the equipment.

[0031] Preferably, the conditions for subcritical water catalytic oxidation are controlled to produce a second wastewater with a TOC ≤ 100 mg / L. More preferably, the conditions for subcritical water catalytic oxidation are controlled to produce a second wastewater with a TOC ≤ 100 mg / L.

[0032] Preferably, the subcritical water catalytic oxidation conditions include a temperature range of 220℃ to 290℃ and a pressure range of 5 to 10 MPa. The selection of temperature and pressure is not arbitrary. For example, when the temperature is 220℃, the pressure value can be flexibly selected within the 5 to 10 MPa range according to the required reaction time, and the same applies when other temperatures are used. Preferably, when a higher temperature is selected, the pressure can be appropriately reduced.

[0033] By setting a minimum TOC for the second wastewater, the duration of the subcritical water catalytic oxidation reaction can be shortened, thus improving wastewater treatment efficiency. When the organic matter concentration decreases to a certain level, if subcritical water catalytic oxidation continues, more stringent control of the reaction conditions is required, such as increasing the reaction temperature and pressure. In this invention, a lower limit for subcritical water catalytic oxidation is set, and subcritical water catalytic oxidation is stopped in a timely manner. Further treatment using subsequent adsorption methods can improve the treatment efficiency of the system.

[0034] The second wastewater obtained from the subcritical water catalytic oxidation reaction is under high temperature and high pressure. In the third step S3, the temperature of the second wastewater is reduced. A heat exchanger can be used to recover the heat from the second wastewater for preheating the first wastewater in the second step. If the temperature of the second wastewater is still high after heat exchange, it can be further cooled by a condenser until it is adjusted to 50℃~60℃. While reducing the temperature of the second wastewater, its pressure needs to be released to normal pressure, usually standard atmospheric pressure. This releases the carbon dioxide, gases, and water vapor generated by the subcritical water catalytic oxidation reaction from the liquid phase, resulting in the third wastewater. In this invention, by controlling the temperature range of the third wastewater to 50℃~60℃, the solubility of sodium chloride is stably maintained between 37~37.3g / 100g water within this range. This maintains a high and stable solubility of sodium chloride, preventing sodium chloride precipitation and equipment blockage.

[0035] The third wastewater still contains some residual organic matter, including small-molecule organic compounds generated by catalytic oxidation, with a TOC ≤ 150 mg / L, requiring further treatment. The third wastewater also contains dissolved catalysts, which also need to be removed.

[0036] In step S4, since all catalysts exhibit the characteristic of precipitation under alkaline conditions, in this invention, the pH of the third wastewater can be adjusted to above 9 using NaOH solution. The catalyst can then be recovered through filtration or centrifugation, and subsequently dissolved in 36%–38% concentrated hydrochloric acid for reuse. Alternatively, the catalyst can be adsorbed using chelating resin, and after adsorption saturation, it can be eluted with 4–6 wt% dilute hydrochloric acid for reuse. The fourth wastewater still retains some organic matter and contains small-molecule organic compounds generated by catalytic oxidation, with a TOC ≤ 150 mg / L.

[0037] In the fifth step S5, the organic matter in the fourth wastewater is adsorbed. Since the organic matter content in the fourth wastewater has been reduced to a low level, such as TOC ≤ 150 mg / L or TOC ≤ 100 mg / L, the catalytic oxidation efficiency for these residual organic matter is much lower than the resin adsorption efficiency. In this invention, a salt-resistant adsorption resin is used to adsorb the organic matter into the fourth wastewater until a sodium chloride solution with TOC ≤ 10 mg / L is obtained. The adsorption resin can be obtained commercially; any resin that is salt-resistant and has adsorption properties for small molecule compounds can be selected. For example, the weakly polar, salt-resistant ether-based carbon ball resin RapadC carbon balls provided by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences.

[0038] In this invention, when the TOC of the wastewater is ≤150 mg / L, adsorption treatment of the residual organic matter can be performed, which can improve the wastewater treatment speed and quickly reduce the TOC value to ≤10 mg / L. Since the residual organic matter content in the fourth wastewater is low, the adsorption treatment process can be completed with less adsorption resin.

[0039] The wastewater treatment method for synthesizing bisphenol A type epoxy resin, as described above, utilizes pure oxygen as the oxidant and strictly controls the amount of oxygen, limiting excess oxygen to within 1.2 times the standard limit. This reduces the amount of gas released during the cooling and depressurization process after the subcritical water catalytic oxidation, thereby reducing the release of water vapor due to gas overflow and preventing sodium chloride supersaturation precipitation. By setting the cooling temperature of the second wastewater between 50 and 60°C, a high solubility of sodium chloride can be maintained, further preventing sodium chloride saturation precipitation. The subcritical water catalytic oxidation treatment yields a second wastewater with a TOC ≤ 150 mg / L, reducing the requirements for temperature and pressure conditions in the catalytic oxidation process, simplifying control, and improving the stability of the reaction process. By following the catalytic oxidation step with adsorption treatment, residual or difficult-to-remove trace amounts of organic matter from the catalytic oxidation process can be further removed, resulting in a rapid and stable sodium chloride solution with a TOC ≤ 10 mg / L. Furthermore, in some embodiments, by recovering the heat from the catalytic oxidation process's output to preheat the feed for the catalytic oxidation process, energy consumption can be reduced. Furthermore, in some embodiments, by setting the second wastewater to 80≤TOC≤100mg / L, the control conditions for catalytic oxidation can be reduced on the one hand, and the amount of organic matter to be treated in subsequent adsorption treatment can be reduced on the other hand.

[0040] Example 1

[0041] 150m³ of wastewater generated from the synthesis of bisphenol A type epoxy resin 3 / day, COD is 12000 mg / L, pH is 8, and sodium chloride mass percentage is 23%.

[0042] Add catalyst CuCl2 at 0.6% of the wastewater mass and oxygen at 1.02 times the COD of the wastewater.

[0043] Add 37%wt concentrated hydrochloric acid to the equalization tank to adjust the pH of the wastewater to 3, add the catalyst and mix evenly, then mix with oxygen through a pipeline and enter the heat exchanger for preheating. After preheating, the wastewater enters the subcritical water catalytic oxidation reaction tower for reaction. The subcritical water catalytic oxidation reaction temperature is 220℃ and the reaction pressure is 5.5MPa. Monitor the TOC value of the oxidized liquid in the reaction tower until it decreases to 100mg / L.

[0044] The oxidizing liquid discharged from the reaction tower was cooled to 50°C through a heat exchanger and condenser, and then reduced to standard atmospheric pressure. The pH was adjusted to 9 with NaOH solution, and the catalyst was recovered by centrifugation. The catalyst was then treated by adsorption using Rapad C carbon balls until a sodium chloride solution with TOC ≤ 10 mg / L was obtained.

[0045] Example 2

[0046] The oxygen content was set to 1.10 times the COD of the wastewater, and other conditions were the same as in Example 1.

[0047] Example 3

[0048] The oxygen content was set to 1.20 times the COD of the wastewater, and other conditions were the same as in Example 1.

[0049] Example 4

[0050] The subcritical water catalytic oxidation reaction temperature was set at 270°C, the reaction pressure at 7.5 MPa, and other conditions were the same as in Example 1.

[0051] Example 5

[0052] The subcritical water catalytic oxidation reaction temperature was set at 290°C, the reaction pressure at 9.8 MPa, and other conditions were the same as in Example 1.

[0053] Comparative Example 1

[0054] The oxygen content was 1.50 times the COD of the wastewater, and other conditions were the same as in Example 1.

[0055] Comparative Example 2

[0056] The oxygen content was 1.00 times the COD of the wastewater, and other conditions were the same as in Example 1.

[0057] The monitoring data for each embodiment and comparative example are shown in Table 1. "~100" indicates that the TOC value is slightly lower than 100.

[0058] Table 1

[0059]

[0060] As can be seen from Examples 1 to 5, the present invention can reduce the temperature, pressure and duration of the oxidation reaction, effectively reduce the processing and manufacturing difficulty of equipment, valves, instruments and pipelines, reduce equipment material consumption and improve the safety of the device.

[0061] As shown in Comparative Example 1, when the oxygen content is greater than 1.20 times the COD, sodium chloride is precipitated before the TOC reaches ≤100 mg / L during the oxidation process. As shown in Comparative Example 2, when the oxygen content is less than 1.02 times the COD, the oxidation time increases, and when the oxidation time is the same as in Example 1, the TOC only decreases to 500 mg / L.

[0062] While numerous embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will occur to those skilled in the art without departing from the spirit and essence of the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. The appended claims are intended to define the scope of protection of the invention and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for treating wastewater generated during the synthesis of bisphenol A type epoxy resin, characterized in that, include: The first step involves adjusting the pH of the wastewater generated from the synthesis of bisphenol A epoxy resin to 1-5, mixing it with a catalyst and oxygen to obtain the first wastewater. The amount of oxygen added is set to be 1.02-1.2 times the COD of the wastewater. The second step is to adjust the temperature and pressure of the first wastewater so that it undergoes a subcritical water catalytic oxidation reaction until a second wastewater with TOC ≤ 150 mg / L is obtained. The third step is to adjust the temperature of the second wastewater to 50℃-60℃ and the pressure to standard atmospheric pressure to obtain the third wastewater; The fourth step is to remove the catalyst from the third wastewater to obtain the fourth wastewater; The fifth step involves adsorption treatment of the fourth wastewater until a sodium chloride solution with TOC ≤ 10 mg / L is obtained.

2. The processing method according to claim 1, characterized in that, The heat from the second wastewater in the third step is used to preheat the first wastewater in the second step.

3. The processing method according to claim 1, characterized in that, In the first step, the catalyst is selected from one or more of CuCl2, CeCl3, FeCl3, MoCl5, CoCl2, NiCl2 and ZnCl2, and the amount of catalyst is 0.1% to 1% of the mass of the wastewater.

4. The processing method according to claim 1, characterized in that, In the second step, the temperature and pressure of the first wastewater are adjusted to keep the first wastewater in a liquid state.

5. The processing method according to claim 1, characterized in that, Adjust the temperature and pressure of the first wastewater to: temperature range of 220℃~290℃, pressure range of 5~10 MPa.

6. The processing method according to claim 1, characterized in that, In the second step, the concentration of the second wastewater is controlled to be 80 mg / L ≤ TOC ≤ 100 mg / L.

7. The processing method according to claim 1, characterized in that, In the fourth step, the catalyst is removed by the following method: The pH of the third wastewater is adjusted to above 9 using NaOH solution, and the catalyst is recovered by filtration or centrifugation. Alternatively, chelating resins can be used to recover the catalyst.

8. The processing method according to claim 1, characterized in that, In the fifth step, the fourth wastewater is treated by adsorption using a salt-resistant adsorption resin.

9. The processing method according to claim 1, characterized in that, In the first step, 36%~38%wt of concentrated hydrochloric acid is added to adjust the pH.

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