Recycling process and recycling system for acetic acid in process water of PTA (pure terephthalic acid) device

Abstract

The invention relates to the field of terephthalic acid production devices, in particular to a system for recovering acetic acid in process water of a PTA (pure terephthalic acid) device, which comprises the following steps: step 1, cooling: cooling the process water of the PTA device to 18-20 DEG C; 2, impurity removal: removing impurities in the process water of the PTA device; step 3, performing primary reverse osmosis, namely performing primary reverse osmosis on the process water of the PTA device to generate primary penetrating fluid and primary retentate, and returning the primary retentate to the PTA mother liquor system for recycling; step 4, performing secondary reverse osmosis, namely performing secondary reverse osmosis on the primary penetrating fluid to generate secondary penetrating fluid and secondary retentate, outputting the secondary penetrating fluid, and returning the secondary retentate to the step 3 to perform the primary reverse osmosis; 5, cold energy recovery: recovering the cold energy of the final produced water for cooling in the step 1; the method has the following beneficial effects that the reverse osmosis membrane group is adopted, the acetic acid in the process water is recovered, and ten thousand tons of acetic acid are recovered every year according to 80t / h.

Description

Technical Field

[0001] The invention relates to the field of terephthalic acid production devices, and in particular to an acetic acid recovery system in process water of a PTA device. Background Art

[0002] PTA, or terephthalic acid, is an organic compound and the largest dicarboxylic acid in production. It is solid at room temperature. It does not melt when heated, but sublimates above 300°C. If heated in a sealed container, it can melt at 427°C. Terephthalic acid is the raw material for producing polyester, especially polyethylene terephthalate (PET).

[0003] In the latest process technology of PTA unit, the discharged process water contains about 2% acetic acid. Acetic acid is an important raw material in the PTA production process. Recycling acetic acid can reduce the demand for fresh acetic acid, thereby improving resource utilization; recycling acetic acid can reduce the production cost of PTA, because the recycled acetic acid can be used again in the production process, reducing the consumption of raw materials and procurement costs; if acetic acid is discharged directly into the environment without treatment, it may cause environmental pollution. Recycling acetic acid can reduce pollution to the environment and meet environmental protection requirements. Therefore, in order to improve resource utilization, reduce production costs and reduce environmental pollution, it is necessary to recycle acetic acid in the process water of PTA unit.

[0004] In the prior art, there is a technology for recovering acetic acid from the process water of a PTA device using a reverse osmosis membrane, but there are the following problems:

[0005] 1. In addition to acetic acid, there are also organic impurities and metal impurities in the process water of the PTA unit. Directly using a reverse osmosis membrane group to separate them will cause the reverse osmosis membrane to become fouled quickly, which not only reduces the recovery efficiency of acetic acid, but also increases production costs;

[0006] 2. Usually, a set of reverse osmosis membrane groups can only recover part of the acetic acid, and a large amount of acetic acid cannot be recovered, resulting in waste; the prior art also uses a technology of using multiple reverse osmosis membrane groups in series, but the cost of a set of reverse osmosis modules is as high as one million, and needs to be replaced regularly, so the cost of using multiple reverse osmosis membrane groups in series for recycling is very high. Summary of the invention

[0007] The object of the present invention is to provide a process and system for recovering acetic acid in process water of a PTA device, which have the characteristics of being able to fully recover acetic acid in process water of the PTA device and saving costs.

[0008] The above technical objectives of the present invention are achieved through the following technical solutions: A process for recovering acetic acid from process water of a PTA device, comprising the following steps:

[0009] Step 1: Cool down the process water of the PTA unit to 18°C ​​to 20°C;

[0010] Step 2: removing impurities in the process water of the PTA device, and removing organic impurities, metal impurities and impurity ions in the process water of the PTA device in turn;

[0011] Step 3, primary reverse osmosis, the process water of the PTA device undergoes primary reverse osmosis to produce primary permeate and primary retentate, the primary permeate is water containing 0.6% acetic acid, the primary retentate is acetic acid, and the primary retentate is returned to the PTA mother liquor system for recycling;

[0012] Step 4, secondary reverse osmosis, the primary permeate is subjected to secondary reverse osmosis to produce secondary permeate and secondary retentate, the secondary permeate is the final produced water, the secondary retentate is dilute acid, part of the secondary permeate is mixed with the primary permeate to dilute the acetic acid concentration of the primary permeate, the other secondary permeate is output, and the secondary retentate is returned to step 3 to perform primary reverse osmosis;

[0013] Step 5: Recovering cold energy: Recovering the cold energy of the final produced water for cooling the process water of the PTA unit in step 1;

[0014] Step six: water treatment and / or water reuse: the final produced water is discharged after sewage treatment and / or the final produced water is used for industrial water spraying of the PTA device.

[0015] Preferably, in step one, the cold capacity in the final produced water is first used to cool the process water of the PTA device, and ultrasonic impurity removal is used to remove organic impurities.

[0016] Preferably, electromagnetic impurity removal is used to remove metal impurities, and the strong magnetic electrode applied is 16000GS.

[0017] Preferably, resin filters installed in series are used to remove impurity ions in the process water, and the resin filters are acid-washed and water-washed to restore performance after offline isolation.

[0018] A system for recovering acetic acid in process water of a PTA device comprises a feed pipeline, which is sequentially connected to a cooling unit, an impurity removal unit and a reverse osmosis unit; a discharge pipeline of the reverse osmosis unit is connected to a sewage treatment unit and / or an industrial water spray unit; the reverse osmosis unit comprises a primary pressure pump and a primary reverse osmosis membrane group; the retentate discharge of the primary reverse osmosis membrane group is connected to a PTA mother liquor system; the permeate discharge is sequentially connected to a primary permeate storage tank, a secondary pressure pump and a secondary reverse osmosis membrane group; the retentate discharge of the secondary reverse osmosis membrane group is connected to the secondary retentate pressure pump and then to the feed end of the primary reverse osmosis membrane group; the permeate discharge end is connected to a secondary permeate storage tank and a produced water delivery pump, and then is connected to the sewage treatment unit and / or the industrial water spray unit; the permeate discharge of the secondary reverse osmosis membrane group is also connected to the primary permeate storage tank.

[0019] Preferably, the cooling unit includes an energy recovery heat exchanger and a chilled water heat exchanger, the process water of the PTA device passes through the energy recovery heat exchanger as a heat medium, and the final produced water output by the produced water delivery pump passes through the energy recovery heat exchanger as a cold medium.

[0020] Preferably, the impurity removal unit comprises an organic filter, a metal filter and a resin filter membrane.

[0021] Preferably, the resin filter membrane comprises filter membrane one, filter membrane two and filter membrane three connected in series, and isolation pipelines are respectively connected in parallel to filter membrane one, filter membrane two and filter membrane three for isolating them separately.

[0022] Preferably, isolation pipelines are respectively connected in parallel to the primary reverse osmosis membrane group and the secondary reverse osmosis membrane group for isolating and disconnecting them separately.

[0023] Preferably, a valve one is provided between the primary booster pump and the primary reverse osmosis membrane group; the discharge end of the primary booster pump is connected to the feed end of the secondary reverse osmosis membrane group through a valve two, the discharge end of the primary permeate storage tank is connected to the feed end of the produced water delivery pump through a valve three, a valve four is connected between the discharge end of the secondary reverse osmosis membrane group and the primary permeate storage tank, the discharge end of the secondary reverse osmosis membrane group is connected to the PTA mother liquor system through a valve five, and a valve six is ​​connected between the secondary reverse osmosis membrane group and the secondary permeate storage tank.

[0024] In summary, the present invention has the following beneficial effects:

[0025] 1. Use electromagnetic and ultrasonic impurity removal to effectively reduce the content of metal impurities and organic impurities in process water and ensure the service life of the membrane core of the reverse osmosis unit;

[0026] 2. Use reverse osmosis membrane group to recover acetic acid in process water. Based on the input of 80t / h, 10,000 tons of acetic acid can be recovered annually;

[0027] 3. The process water is subjected to reverse osmosis twice to fully recover the acetic acid in the process water;

[0028] 4. Two reverse osmosis membrane groups are used, each group can be isolated separately, and the use order of the two reverse osmosis membrane groups can be switched according to demand, which can achieve a better recovery level while extending the service life of the membrane core and reducing costs;

[0029] 5. The process water treated by reverse osmosis membrane group can be used for PTA device spraying, replacing the original industrial water, which can save 630,000 tons of industrial water every year;

[0030] 6. Use process water reuse technology to replace PTA unit industrial water with water treated by reverse osmosis;

[0031] 7. The present invention recovers the cold water in the final water produced after reverse osmosis through a heat exchanger for reuse, thus saving energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the process flow chart of Example 1;

[0033] Figure 2 is a schematic diagram of Example 2;

[0034] Figure 3 is a schematic diagram of the resin filter membrane in Example 2;

[0035] Figure 4 is a schematic diagram of the state of Example 3 before switching;

[0036] Figure 5 This is a schematic diagram of the state of Example 3 after switching.

[0037] In the figure, 1. feed pipeline; 11. energy recovery heat exchanger; 12. chilled water heat exchanger; 21. organic filter; 22. metal filter; 23. resin filter membrane; 231. filter membrane one; 232. filter membrane two; 233. filter membrane three; 31. primary booster pump; 32. primary reverse osmosis membrane group; 33. PTA mother liquor system; 34. primary permeate storage tank; 35. secondary booster pump; 36. secondary reverse osmosis membrane group; 37. secondary retentate booster pump; 38. secondary permeate storage tank; 39. produced water delivery pump; 4. sewage treatment unit; 5. industrial water spray unit; 41. valve one; 42. valve two; 43. valve three; 44. valve four; 45. valve five; 46. valve six. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0039] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

[0040] Embodiment 1:

[0041] A process for recovering acetic acid from process water of a PTA unit, such as Figure 1 As shown, the following steps are included:

[0042] Step 1: Cooling down. The temperature of the process water of the PTA device is 35°C to 40°C. First, the final produced water produced in the method is used to exchange heat with the process water of the PTA device to initially reduce the temperature of the process water. Then, the process water is cooled by a chilled water heat exchanger to cool the process water of the PTA device to 18°C ​​to 20°C.

[0043] Step 2: remove impurities from the process water of the PTA device. Ultrasonic impurity removal technology and electromagnetic impurity removal technology are used in turn to remove organic impurities and metal impurities in the process water. The strong magnetic electrode applied during electromagnetic impurity removal is 16000GS. The filtered process water passes through a resin filter membrane to remove impurity ions in the process water. The resin filter membrane adopts a series layout. After saturation, the resin filter membrane is isolated offline by crossing the line, and is regenerated and restored to performance after acid washing and water washing.

[0044] Step 3, primary reverse osmosis, the process water of the PTA device undergoes primary reverse osmosis to produce primary permeate and primary retentate, the primary permeate is water containing 0.6% acetic acid, the primary retentate is acetic acid, and the primary retentate is returned to the PTA mother liquor system for recycling;

[0045] Step 4, secondary reverse osmosis, the primary permeate is subjected to secondary reverse osmosis to produce secondary permeate and secondary retentate, the secondary permeate is the final produced water, the secondary retentate is dilute acid, a part of the secondary permeate is output, the other part of the secondary permeate is finally produced water and mixed with the primary permeate, diluting the acetic acid concentration of the primary permeate, and returning the secondary retentate to step 3 to perform primary reverse osmosis;

[0046] Step 5: Recovering cold energy: Recovering the cold energy of the final water produced by the secondary permeate and using it for cooling the process water of the PTA unit in step 1;

[0047] Step six, water treatment and water reuse, the secondary permeate after cold recovery is discharged after sewage treatment, and the final water can also be used for industrial water spraying of PTA device according to usage requirements.

[0048] Embodiment 2:

[0049] A PTA unit process water acetic acid recovery system, such as Figure 2 As shown, it includes a feed pipeline 1, which is connected to a cooling unit, a decontamination unit, and a reverse osmosis unit in sequence. The discharge pipeline of the reverse osmosis unit is connected to a sewage treatment unit 4 and an industrial water spray unit 5.

[0050] The reverse osmosis unit includes a primary booster pump 31 and a primary reverse osmosis membrane group 32. The retentate discharge of the primary reverse osmosis membrane group 32 is connected to the PTA mother liquor system 33, and the permeate discharge is sequentially connected to the primary permeate storage tank 34, the secondary booster pump 35, and the secondary reverse osmosis membrane group 36. The retentate discharge of the secondary reverse osmosis membrane group 36 is connected to the secondary retentate booster pump 37 and then to the feed end of the primary reverse osmosis membrane group 32, and the permeate discharge end is connected to the secondary permeate storage tank 38, the produced water delivery pump 39, as well as the sewage treatment unit 4 and the industrial water spray unit 5. The permeate discharge of the secondary reverse osmosis membrane group is also connected to the primary permeate storage tank 34.

[0051] The impurity removal unit includes an organic filter 21, a metal filter 22, and a resin filter membrane 23. The organic filter 21 is an ultrasonic filter. The metal filter 22 is an electromagnetic impurity removal filter, wherein the strong magnetic electrode applied during electromagnetic impurity removal is 16000GS. The resin filter membrane 23 is installed in series, such as Figure 3 As shown, there are three sets, namely filter membrane one 231, filter membrane two 232, and filter membrane three 233. Each set is equipped with an isolation pipeline connected across it for easy isolation.

[0052] The cooling unit includes an energy recovery heat exchanger 11 and a chilled water heat exchanger 12. The process water of the PTA unit passes through the energy recovery heat exchanger 11 as a heat medium, and the final produced water output by the produced water delivery pump 39 passes through the energy recovery heat exchanger 11 as a cold medium. The temperature of the chilled water introduced into the chilled water heat exchanger 12 is 18°C ​​to 20°C.

[0053] Working principle:

[0054] In the latest process technology of the PTA device, the effluent process water contains about 2% acetic acid. The effluent process water is introduced into the energy recovery heat exchanger 11 and the chilled water heat exchanger 12 to reduce the process water temperature to 18°C ​​to 20°C, and then passes through the organic filter 21, the metal filter 22 and the resin filter membrane 23 to remove organic matter, metal impurities and impurity ions in the process water. The process water is pressurized by the primary booster pump 31 and sent to the primary reverse osmosis membrane group 32. The primary permeate is water (containing about 0.6% acetic acid), and the retentate is acetic acid. The acetic acid is returned to the PTA mother liquor system 33 for recycling. The primary permeate enters the primary permeate storage tank 34 for buffering, and then is sent to the secondary reverse osmosis membrane group 36 through the secondary booster pump 35 to further recover the acetic acid. The secondary permeate is the final produced water, and the retentate is dilute acid. The dilute acid passes through the secondary retentate booster pump 37 and returns to the primary reverse osmosis membrane group 32 to purify the acetic acid. A portion of the final produced water enters the secondary permeate storage tank 38 for buffering, is pressurized by the produced water delivery pump 39, and then passes through the energy recovery heat exchanger 11 and the process water for heat exchange to recover heat, and is finally sent to the industrial water spray unit 5 or the sewage treatment unit 4. Another portion of the final produced water enters the primary permeate storage tank 34 as the diluted secondary inlet water to dilute the acetic acid therein.

[0055] Embodiment 3:

[0056] This embodiment is basically the same as embodiment 2, except that Figure 4 , Figure 5 As shown, a valve 1 41 is provided between the primary booster pump 31 and the primary reverse osmosis membrane group 32; the discharge end of the primary booster pump 31 is connected to the feed end of the secondary reverse osmosis membrane group 36 through a valve 2 42, the discharge end of the primary permeate storage tank 34 is connected to the feed end of the produced water delivery pump 39 through a valve 3 43, the pipeline between the permeate discharge end of the secondary reverse osmosis membrane group 36 and the primary permeate storage tank 34 is connected with a valve 4 44, the discharge end of the retentate of the secondary reverse osmosis membrane group 36 is connected to the PTA mother liquor system 33 through a valve 5 45, and the permeate discharge end of the secondary reverse osmosis membrane group 36 is connected to the secondary permeate storage tank 38 with a valve 6 46. The secondary retentate booster pump 37 is connected to the permeate discharge end of the secondary reverse osmosis membrane group 36. An isolation pipeline is connected across the primary reverse osmosis membrane group 32 and the secondary reverse osmosis membrane group 36.

[0057] Working principle: The service life of the membrane core of the reverse osmosis membrane group is limited and must be replaced every certain period of time. Since the replacement of the membrane core requires downtime, the general manufacturer will arrange it during the annual maintenance. Therefore, it is necessary to extend the service life of the membrane core so that the membrane core can be used at least until the date of the annual maintenance. The staff found in actual production that the first-stage reverse osmosis membrane group 32 always reaches the life limit earlier than the second-stage reverse osmosis membrane group 36. This is because the impurity removal unit in the front section cannot guarantee that all impurities are 100% removed. This is an objective law and cannot be avoided. The process water from the impurity removal unit first passes through the first-stage reverse osmosis membrane group 32, and then passes through the second-stage reverse osmosis membrane group 36, so that the workload of the first-stage reverse osmosis membrane group 32 is greater than that of the second-stage reverse osmosis membrane group 36, so the first-stage reverse osmosis membrane group 32 always reaches the life limit earlier than the second-stage reverse osmosis membrane group 36.

[0058] Before the primary reverse osmosis membrane group 32 reaches its life limit, the system is switched so that the process water from the impurity removal unit first passes through the secondary reverse osmosis membrane group 36 and then passes through the primary reverse osmosis membrane group 32, which can effectively extend the service life of the membrane core of the primary reverse osmosis membrane group 32. The specific operation is as follows:

[0059] Before switching, Figure 4 As shown, valve one 41, valve four 44, valve six 46 are open, and valve two 42, valve three 43, valve five 45 are closed. The flow of process water in the system is as described in Example 2, which will not be repeated here.

[0060] When switching, valve one 41, valve four 44, valve six 46 are closed, valve two 42, valve three 43, valve five 45 are opened, and the secondary retentate booster pump 37 is connected to the permeate outlet of the secondary reverse osmosis membrane group 36. Figure 5 As shown, after the process water leaves the impurity removal unit, it first enters the secondary reverse osmosis membrane group 36, the retentate enters the PTA mother liquor system 33, the permeate enters the primary reverse osmosis membrane group 32 through the secondary retentate pressure pump 37, and the retentate and permeate of the primary reverse osmosis membrane group 32 enter the PTA mother liquor system 33 and the primary permeate storage tank 34 respectively. The primary permeate storage tank 34 contains the final produced water, which is pressurized by the produced water delivery pump 39 and then passes through the energy recovery heat exchanger 11 and the process water to recover heat, and finally is sent to the industrial water spray unit 5 or the sewage treatment unit 4.

Claims

1. A process for recovering acetic acid from process water of a PTA device, characterized in that: The following steps are involved: Step 1: Cool down the process water of the PTA unit to 18°C ​​to 20°C; Step 2: removing impurities in the process water of the PTA device, and removing organic impurities, metal impurities and impurity ions in the process water of the PTA device in turn; Step 3, primary reverse osmosis, the process water of the PTA device undergoes primary reverse osmosis to produce primary permeate and primary retentate, the primary permeate is water containing 0.6% acetic acid, the primary retentate is acetic acid, and the primary retentate is returned to the PTA mother liquor system for recycling; Step 4, secondary reverse osmosis, the primary permeate is subjected to secondary reverse osmosis to produce secondary permeate and secondary retentate, the secondary permeate is the final produced water, the secondary retentate is dilute acid, part of the secondary permeate is mixed with the primary permeate to dilute the acetic acid concentration of the primary permeate, the other secondary permeate is output, and the secondary retentate is returned to step 3 to perform primary reverse osmosis; Step 5: Recovering cold energy: Recovering the cold energy of the final produced water for cooling the process water of the PTA unit in step 1; Step six: water treatment and / or water reuse: the final produced water is discharged after sewage treatment and / or the final produced water is used for industrial water spraying of the PTA device.

2. The process for recovering acetic acid from process water of a PTA device according to claim 1, characterized in that: Ultrasonic impurities are removed by ultrasonic cleaning.

3. The process for recovering acetic acid from process water of a PTA device according to claim 1, characterized in that: Electromagnetic impurity removal is used to remove metal impurities, and the strong magnetic electrode applied is 16000GS.

4. The process for recovering acetic acid from process water of a PTA device according to claim 1, characterized in that: Impurity ions in process water are removed using resin membranes installed in series. After offline isolation, the resin membranes are acid-washed and water-washed to restore performance.

5. A system for recovering acetic acid from process water of a PTA device, characterized in that: The invention comprises a feed pipeline (1), which is sequentially connected to a cooling unit, a decontamination unit, and a reverse osmosis unit; a discharge pipeline of the reverse osmosis unit is connected to a sewage treatment unit (4) and / or an industrial water spray unit (5); the reverse osmosis unit comprises a primary pressure pump (31) and a primary reverse osmosis membrane group (32); the retentate discharge of the primary reverse osmosis membrane group (32) is connected to a PTA mother liquor system (33); the permeate discharge is sequentially connected to a primary permeate storage tank (34), a secondary pressure pump (35) and a secondary pressure pump (36). ), a secondary reverse osmosis membrane group (36), the retentate outlet of the secondary reverse osmosis membrane group (36) is connected to a secondary retentate pressure pump (37) and then connected to the feed end of the primary reverse osmosis membrane group (32), the permeate outlet of the secondary reverse osmosis membrane group (36) is connected to a secondary permeate storage tank (38) and a produced water delivery pump (39), and then connected to a sewage treatment unit (4) and / or an industrial water spray unit (5), and the permeate outlet of the secondary reverse osmosis membrane group (36) is also connected to a primary permeate storage tank (34).

6. The acetic acid recovery system in process water of a PTA device according to claim 5, characterized in that: The cooling unit comprises an energy recovery heat exchanger (11) and a chilled water heat exchanger (12); process water of the PTA device passes through the energy recovery heat exchanger (11) as a heat medium, and final produced water output by a produced water delivery pump (39) passes through the energy recovery heat exchanger (11) as a cold medium.

7. The acetic acid recovery system in process water of a PTA device according to claim 6, characterized in that: The impurity removal unit comprises an organic filter (21), a metal filter (22) and a resin filter membrane (23).

8. The acetic acid recovery system in process water of a PTA device according to claim 7, characterized in that: The resin filter membrane (23) comprises a filter membrane 1 (231), a filter membrane 2 (232), and a filter membrane 3 (233) connected in series. Isolation pipelines are respectively connected in parallel to the filter membrane 1 (231), the filter membrane 2 (232), and the filter membrane 3 (233) for isolating them separately.

9. The acetic acid recovery system in process water of a PTA device according to claim 8, characterized in that: Isolation pipelines are respectively connected in parallel to the primary reverse osmosis membrane group (32) and the secondary reverse osmosis membrane group (36) for isolating and disconnecting them separately.

10. The acetic acid recovery system in process water of a PTA device according to claim 9, characterized in that: A valve one (41) is provided between the primary booster pump (31) and the primary reverse osmosis membrane group (32); the discharge end of the primary booster pump (31) is connected to the feed end of the secondary reverse osmosis membrane group (36) via a valve two (42); the discharge end of the primary permeate storage tank (34) is connected to the feed end of the produced water delivery pump (39) via a valve three (43); a valve four (44) is connected between the discharge end of the secondary reverse osmosis membrane group (36) and the primary permeate storage tank (34); the discharge end of the secondary reverse osmosis membrane group (36) is connected to the PTA mother liquor system (33) via a valve five (45); and a valve six (46) is connected between the secondary reverse osmosis membrane group (36) and the secondary permeate storage tank (38).

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