Process for treating pta production wastewater

Abstract

The application discloses a PTA production wastewater treatment process, comprising the following steps: adjusting the pH of PTA production wastewater to 8-12, adding a flocculating agent, stirring at a speed of 200-400 rpm for 20-40 min, making the solution completely precipitate, removing the precipitate by filtration after the flocculation is completed, and obtaining primary treatment water; adding an adsorbent to the primary treatment water for adsorption, removing the adsorbent by filtration after the adsorption is completed, and obtaining secondary treatment water; and first passing the secondary treatment water through a ceramic microfiltration membrane, and then entering an ultrafiltration unit for ultrafiltration, and obtaining final effluent water. The process can effectively remove pollutants in water, and realizes zero discharge of pollution.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and more specifically, relates to a PTA production wastewater treatment process. Background Technology

[0002] Purified terephthalic acid (PTA) is an important chemical intermediate, serving as a raw material or intermediate in the production of polyester fibers, plasticizers, pesticides, and dyes. It is produced by oxidizing p-xylene as a raw material, acetic acid as a solvent, and cobalt acetate, manganese acetate, and bromoethane as catalysts under specific temperature and pressure conditions using air to produce crude terephthalic acid (TA), which is then further refined into purified terephthalic acid (PTA). Statistics show that the wastewater discharge for producing 1 ton of PTA is generally 3.3–5.6 m³. 3 Of this, refining wastewater accounts for 90%. Analysis shows that PTA production wastewater has a complex composition, with the main pollutants being acetic acid, trimellitic acid, benzoic acid, isophthalic acid, p-hydroxybenzaldehyde, terephthalic acid, and p-methylbenzoic acid, which are difficult-to-biodegrade chemical wastewaters.

[0003] Currently, there are many methods for treating PTA wastewater, including physicochemical and biological treatment methods. Initially, researchers developed and studied wastewater treatment using ion exchange, osmosis, and reverse osmosis technologies, but these were not adopted later due to their high cost. In physicochemical methods, acid precipitation, flocculation, and filtration are mainly used in pretreatment. Aerobic treatment methods cannot be used alone due to their inability to handle high-concentration wastewater and the problem of sludge bulking.

[0004] Existing technologies also disclose methods for treating PTA wastewater. For example, Chinese invention patent application number 200910177342.X discloses a method for treating purified terephthalic acid (PTA) wastewater, including the following steps: 1. Adjusting the pH of the purified wastewater to 4-5 to dissolve the fine suspended solids; 2. Sending the purified wastewater into a resin adsorption unit to remove cobalt and manganese ions from the water. After the resin adsorption unit operates for a certain period of time, it is regenerated to recover the cobalt and manganese ions; 3. Treating the purified wastewater with a primary reverse osmosis membrane, and then treating the permeate with a secondary reverse osmosis membrane, with the concentrate discharged into a wastewater treatment plant; 4. Treating the permeate from the primary reverse osmosis membrane with a secondary reverse osmosis membrane, returning the treated permeate to the production system, and returning the concentrate to the inlet of the primary reverse osmosis membrane. This method uses a combination of resin adsorption and multi-stage osmosis, resulting in high costs. For example, Chinese invention patent application number 201210576803.2 discloses a water reuse treatment process for wastewater from purified terephthalic acid (PTA) production, including the following steps: PTA production wastewater is treated by removing TA, suspended solids, and colloids, followed by anaerobic treatment, then treatment through an oxidation ditch and MBR membrane, then secondary reverse osmosis treatment, and finally electro-desalination treatment; the removal of TA, suspended solids, and colloids is a coagulation and sedimentation reaction; the anaerobic treatment is performed through an internal circulation anaerobic reactor; the oxidation ditch is a Carrousel oxidation ditch or an Orbel oxidation ditch; the MBR membrane is selected from polyethylene, polyethersulfone, and polyvinylidene fluoride; the reverse osmosis membrane is selected from cellulose acetate membrane or polyamide composite membrane. This treatment process is complex and difficult to operate. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide a PTA production wastewater treatment process. The process of this invention can effectively remove pollutants from the water, achieving zero pollution discharge.

[0006] The objective of this invention and the technical problem it solves are achieved by the following technical solutions.

[0007] One aspect of the present invention provides a PTA production wastewater treatment process, comprising the following steps:

[0008] After adjusting the pH of the PTA production wastewater to 8-12, add flocculant and stir at 200-400 rpm for 20-40 minutes to allow the solution to settle completely. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0009] The water treated in the first stage is added to an adsorbent for adsorption. After adsorption is complete, the adsorbent is removed by filtration to obtain the water treated in the second stage.

[0010] The water treated in the above-mentioned secondary process is first passed through a ceramic microfiltration membrane, and then enters an ultrafiltration unit for ultrafiltration to obtain the final effluent.

[0011] Preferably, the preparation method of the flocculant is as follows: a polyvinyl alcohol aqueous solution with a concentration of 0.1-0.5 g / mL and a chitosan aqueous solution with a concentration of 1-1.5 g / mL are mixed at a volume ratio of 1:3-5, and an anionic surfactant and potassium persulfate are added. The mixture is heated at 60-100℃ for 2-4 hours. After the reaction is completed, the product is filtered, washed, dried, and pulverized through a 200-400 mesh sieve to obtain the flocculant.

[0012] Preferably, the anionic surfactant and potassium persulfate are added in a mass ratio of 1:0.2-0.5.

[0013] Preferably, the anionic surfactant is selected from one or more of sodium lignosulfonate, ammonium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, or potassium lignosulfonate.

[0014] Preferably, the flocculant is added at a rate of 400-1000 mg per 1 L of wastewater.

[0015] Preferably, the adsorbent is prepared by the following method:

[0016] Silver nitrate and antimony chloride are dissolved in a chloroform / organic alcohol / aqueous solution (volume ratio 1:2-8:50) at a mass ratio of 1:0.05-0.1 to obtain a modified solution.

[0017] Take an appropriate amount of PS emulsion, then centrifuge at 3000-5000 r / h for 6-8 h and remove the supernatant to obtain the bottom precipitate. Dry the precipitate at 80-100℃ overnight to obtain an ordered PS template.

[0018] The PS template obtained above is immersed in a modified solution of 0.2-0.5 g / mL at a temperature between 40-50℃ for 12-24 hours, then removed and dried, and then calcined at 400-800℃ for 2-6 hours. After the reaction is completed, it is cooled to room temperature to obtain the adsorbent.

[0019] Preferably, the organic alcohol includes any one of methanol, ethanol, ethylene glycol, and glycerol.

[0020] Preferably, the adsorbent is added at a rate of 1-3g per 1L of wastewater.

[0021] Preferably, the ceramic microfiltration membrane has the following conditions: pore size 0.02-0.5 μm and operating pressure 0.1-0.3 MPa.

[0022] Preferably, the ultrafiltration operating flux is 30-40 L / h, the operating pressure is 0.1-0.3 MPa, the operating mode is cross-flow filtration, the ultrafiltration operating time is 30 min, the backwashing time is 30 s, the rinsing time is 30 s, and the molecular weight cutoff is 500-1000 Da.

[0023] By employing the above technical solution, the present invention has at least the following advantages: The wastewater treatment process for purified terephthalic acid (PTA) production of the present invention has a simple flow process, low construction and operating costs, can effectively treat PTA production wastewater, produces high-quality effluent, greatly reduces the amount of clean water used and wastewater discharged by PTA production plants, is easy to promote and apply, and has excellent application prospects. The treatment process of the present invention integrates multiple technologies such as flocculation, adsorption, and ultrafiltration, which can improve the quality of effluent, achieve zero pollution discharge, and save energy and protect the environment.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0025] To make the technical means, creative features, achieved objectives, and effects of this invention readily understandable, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0026] Example 1: Preparation of flocculant I

[0027] Mix 100 mL of 0.3 g / mL polyvinyl alcohol aqueous solution and 400 mL of 1.25 g / mL chitosan aqueous solution, then add 1 g of sodium lignosulfonate and 0.35 g of potassium persulfate and heat at 80 °C for 3 h. After the reaction is complete, the product is filtered, washed, dried, and pulverized through a 200-400 mesh sieve to obtain flocculant I.

[0028] Example 2: Preparation of Flocculant II

[0029] Mix 100 mL of 0.5 g / mL polyvinyl alcohol aqueous solution and 500 mL of 1.5 g / mL chitosan aqueous solution, then add 1 g of ammonium lignosulfonate and 0.5 g of potassium persulfate and heat at 60 °C for 4 h. After the reaction is complete, the product is filtered, washed, dried, and pulverized through a 200-400 mesh sieve to obtain flocculant II.

[0030] Example 3: Preparation of Flocculant II

[0031] Mix 100 mL of 0.1 g / mL polyvinyl alcohol aqueous solution and 300 mL of 1 g / mL chitosan aqueous solution, then add 1 g of calcium lignosulfonate and 0.5 g of potassium persulfate and heat at 100 °C for 2 h. After the reaction is complete, the product is filtered, washed, dried, and pulverized through a 200-400 mesh sieve to obtain flocculant III.

[0032] Example 4: Preparation of Adsorbent A

[0033] 100g of silver nitrate and 7.5g of antimony chloride were dissolved in 400mL of a chloroform / methanol / water solution (volume ratio 1:5:50) and mixed thoroughly until completely dissolved to obtain a modified solution. An appropriate amount of PS emulsion was taken, and then centrifuged at 4000r / h for 7h. The supernatant was removed, and the bottom precipitate was obtained. The precipitate was dried overnight at 90℃ to obtain an ordered PS template. The obtained PS template was immersed in a 0.35g / mL modified solution at a temperature between 45℃ and 18h, then removed and dried. It was then calcined at 600℃ for 4h. After the reaction was completed, it was cooled to room temperature to obtain adsorbent A.

[0034] Example 5: Preparation of Adsorbent B

[0035] 100g of silver nitrate and 10g of antimony chloride were dissolved in 500mL of a chloroform / ethanol / water solution (volume ratio 1:2:50) and mixed thoroughly until completely dissolved to obtain a modified solution. An appropriate amount of PS emulsion was taken, and then centrifuged at 3000r / h for 8h. The supernatant was removed, and the bottom precipitate was obtained. The precipitate was dried overnight at 80℃ to obtain an ordered PS template. The obtained PS template was immersed in a 0.5g / mL modified solution at a temperature between 40℃ and 24h, then removed and dried. It was then calcined at 400℃ for 6h. After the reaction was completed, it was cooled to room temperature to obtain the adsorbent B.

[0036] Example 6: Preparation of Adsorbent C

[0037] 100g of silver nitrate and 5g of antimony chloride were dissolved in 300mL of a chloroform / methanol / water solution (volume ratio 1:8:50) and mixed thoroughly until completely dissolved to obtain a modified solution. An appropriate amount of PS emulsion was taken, and then centrifuged at 5000 r / h for 6 h. The supernatant was removed, and the bottom precipitate was obtained. The precipitate was dried overnight at 100℃ to obtain an ordered PS template. The obtained PS template was immersed in a 0.2g / mL modified solution at a temperature between 50℃ and 12 h, then removed and dried. It was then calcined at 800℃ for 2 h. After the reaction was completed, it was cooled to room temperature to obtain the adsorbent C.

[0038] Example 7: PTA Production Wastewater Treatment Process

[0039] S1: After adjusting the pH of the PTA production wastewater to 8-12, add flocculant I at a rate of 800 mg / L and stir at 300 rpm for 30 minutes to allow the solution to settle completely. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0040] S2: Add adsorbent A to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption is complete, filter to remove the adsorbent and obtain secondary treated water.

[0041] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0042] Example 8: PTA Production Wastewater Treatment Process

[0043] S1: After adjusting the pH of the PTA production wastewater to 8-12, add flocculant II at a rate of 800 mg / L and stir at 300 rpm for 30 minutes to allow the solution to settle completely. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0044] S2: Add adsorbent C to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption, filter to remove the adsorbent and obtain secondary treated water.

[0045] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0046] Example 9: PTA Production Wastewater Treatment Process

[0047] S1: After adjusting the pH of the PTA production wastewater to 8-12, add flocculant III at a rate of 800 mg / L and stir at 300 rpm for 30 minutes to allow the solution to settle completely. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0048] S2: Add adsorbent B to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption is complete, filter to remove the adsorbent and obtain secondary treated water.

[0049] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0050] Example 10: PTA Production Wastewater Treatment Process

[0051] S1: After adjusting the pH of the PTA production wastewater to 8-12, add polyaluminum chloride at a rate of 800 mg / L and stir at 300 rpm for 30 minutes to allow the solution to completely settle. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0052] S2: Add activated carbon to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption is complete, filter to remove the adsorbent and obtain secondary treated water.

[0053] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0054] Example 11: PTA Production Wastewater Treatment Process

[0055] S1: After adjusting the pH of the PTA production wastewater to 8-12, add polyalumina at a rate of 700 mg / L and stir at 300 rpm for 30 minutes to allow the solution to completely settle. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0056] S2: Add adsorbent A to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption is complete, filter to remove the adsorbent and obtain secondary treated water.

[0057] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0058] Example 12: PTA Production Wastewater Treatment Process

[0059] S1: After adjusting the pH of the PTA production wastewater to 8-12, add flocculant I at a rate of 800 mg / L and stir at 300 rpm for 30 minutes to allow the solution to settle completely. After flocculation, filter to remove the precipitate and obtain primary treated water.

[0060] S2: Add activated carbon to the primary treated water at a concentration of 2 mg / L for adsorption. After adsorption is complete, filter to remove the adsorbent and obtain secondary treated water.

[0061] S3: The above-mentioned secondary treated water is first passed through a 0.02-0.5μm ceramic microfiltration membrane at an operating pressure of 0.2MPa, and then enters the ultrafiltration unit for ultrafiltration (the ultrafiltration unit is equipped with two hollow fiber ultrafiltration membrane modules of type GK-1). The ultrafiltration flux is 35L / h, the operating pressure is 0.2MPa, the operation mode is cross-flow filtration, the ultrafiltration operation time is 30min, the backwash time is 30s, the rinsing time is 30s, the molecular weight cutoff is 500-1000Da, and the final effluent is obtained. The effluent water quality is tested, and the results are shown in Table 1.

[0062] The parameters of the PTA production wastewater in Examples 7-12 were as follows: COD 2567 mg / L, BOD 879 mg / L, SS (suspended solids) 676 mg / L, conductivity 998 μs / cm, acetic acid 448 mg / L, p-methylbenzoic acid 391 mg / L, phthalic acid 15.2 mg / L, terephthalic acid 39.7 mg / L, isophthalic acid 86.2 mg / L, and trimellitic acid 156.82 mg / L.

[0063] Table 1. Statistics on effluent quality of different treatment processes

[0064]

[0065] Note: The organic matter detection in the table above was performed using a Waters-600 high-performance liquid chromatograph (HPLC) from Waters Instruments, Inc. (USA): 717 autosampler, 2996 diode array detector, binary high-pressure gradient pump, 0.45 μm filter membrane for mobile phase filtration, evacuation for 20 min, operating temperature room temperature, and relative humidity 50%. Acetic acid detection was performed using an Agilent Technologies 6890N gas chromatograph (USA): FID detector, injection volume 1 μL, detection temperature 280℃, programmed temperature ramp vaporization injection, and a temperature ramp rate of 10℃ / min. Other items were detected using conventional methods in this field.

[0066] As can be seen from the results in Table 1, the effluent quality of Examples 7-9 is significantly higher than that of Examples 10-12. This demonstrates that the treatment process of the present invention has high efficiency in treating pollutants in PTA wastewater.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the methods and techniques disclosed above without departing from the scope of the present invention to create equivalent embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A PTA production wastewater treatment process characterized by, It comprises the following steps: After adjusting the pH of the PTA production wastewater to 8-12, a flocculating agent is added and stirred at a speed of 200-400 rpm for 20-40 min to make the solution completely precipitate, and after the flocculation is completed, the precipitate is removed by filtration to obtain first treated water; The adsorbent is added to the first treated water for adsorption, and after the adsorption is completed, the adsorbent is removed by filtration to obtain second treated water; The second treated water is first filtered through a ceramic microfiltration membrane and then subjected to ultrafiltration in an ultrafiltration unit to obtain final effluent; The preparation method of the flocculating agent is as follows: a polyvinyl alcohol aqueous solution with a concentration of 0.1-0.5 g / mL and a chitosan aqueous solution with a concentration of 1-1.5 g / mL are mixed according to a volume ratio of 1:3-5, and then an anionic surfactant and potassium persulfate are added and heated at 60-100 ℃ for 2-4 h, after the reaction is completed, the product is sequentially subjected to filtration, washing, drying, and crushing through a 200-400 mesh sieve to obtain the flocculating agent; The preparation method of the adsorbent is as follows: Silver nitrate and antimony chloride are dissolved in a solution of chloroform: organic alcohol: water in a volume ratio of 1:2-8:50 according to a mass ratio of 1:0.05-0.1, and uniformly mixed until completely dissolved to obtain a modified solution; An appropriate amount of PS emulsion is taken, and then the upper clear liquid is removed after centrifugation at 3000-5000 r / h for 6-8 h to obtain a bottom precipitate, which is dried at 80-100 ℃ overnight to obtain PS templates with ordered arrangement; The PS templates obtained above are soaked in the modified solution with a temperature of 40-50 ℃ for 12-24 h, taken out and dried, and then calcined at 400-800 ℃ for 2-6 h, and after the reaction is completed, it is cooled to room temperature to obtain the adsorbent.

2. The process of claim 1, wherein, The anionic surfactant and potassium persulfate are added in a mass ratio of 1:0.2-0.

5.

3. The process of claim 1, wherein, The anionic surfactant is selected from a mixture of one or more of sodium lignosulfonate, ammonium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, or potassium lignosulfonate.

4. The process of claim 1, wherein, The flocculating agent is added in an amount of 400-1000 mg per 1 L of wastewater.

5. The process of claim 1 wherein, The organic alcohol includes any one of methanol, ethanol, ethylene glycol, or glycerol.

6. The process of claim 1, wherein, The adsorbent is added in an amount of 1-3 g per 1 L of wastewater.

7. The process of claim 1 wherein, The ceramic microfiltration membrane has a pore size of 0.02-0.5 μm and an operating pressure of 0.1-0.3 Mpa.

8. The process of claim 1 wherein, The ultrafiltration operating flux is 30-40 L / h, the operating pressure is 0.1-0.3 Mpa, the operating mode adopts cross-flow filtration mode, the ultrafiltration operating time is 30 min, the backwashing time is 30 s, the flushing time is 30 s, and the molecular weight cut-off is 500-1000 Da.

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