An oxidation process water purification system and method of use thereof

Abstract

The present application relates to the production field of purified terephthalic acid, and particularly relates to an oxidation process water purification treatment system and a use method thereof, which comprises an extraction tower and a rectifying device, characterized in that a separation device is arranged between the extraction tower and the rectifying device, the separation device comprises: a cooling crystallization device, a feed end of the cooling crystallization device is connected with a raffinate discharge end of the extraction tower, and the cooling crystallization device is used for cooling, crystallizing and filtering PT acid in the raffinate; a heat exchanger, a tube side feed end of the heat exchanger is connected with a discharge end of the cooling crystallization device, and the heat exchanger is used for heating the raffinate; and a filter, a feed end of the filter is connected with a tube side discharge end of the heat exchanger, and a discharge end of the filter is connected with a feed end of the rectifying device, and the filter is used for filtering residual PT acid crystallization, and the present application has the following beneficial effects: the separation device is arranged between the extraction tower and the rectifying device, the raffinate discharged from the extraction tower is cooled, crystallized and filtered, the PT acid content of the raffinate is reduced, and the product quality is improved.

Description

Technical Field

[0001] This invention relates to the field of purified terephthalic acid production, and particularly to an oxidation process water purification system and its usage method. Background Technology

[0002] Purified terephthalic acid (PTA) is a major raw material for the production of polyester. It can be directly esterified and polycondensed with ethylene glycol to obtain polyester, and can also be used to make engineering polyester plastics. It is also used as a raw material for plasticizers and a dye intermediate. Its production process uses p-xylene (PX) as a raw material, which is oxidized in the liquid phase to produce crude terephthalic acid, which is then purified by hydrogenation, crystallization, separation, and drying to obtain purified terephthalic acid.

[0003] The PTA production system consists of an oxidation section and a refining section. Before the product enters the oxidation section, such as... Figure 1 As shown, a conventional packed tower is used to extract PTA mother liquor, which contains 98% water, 1.5% acetic acid, 0.2% p-toluic acid (hereinafter referred to as PT acid), 0.2% PTA, and 0.1% other impurities. PX is used as the extractant to extract PT acid and benzoic acid from the PTA mother liquor into the PX and then into the oxidation reactor for recovery. The raffinate (mother liquor) is then distilled in an oxidative distillation tower and recycled back into the process water system.

[0004] The raffinate contains approximately 80 ppm of PT acid, and the PT acid content indirectly affects product quality. Reducing the PT acid content in the raffinate can effectively improve product quality and reduce equipment consumption. Therefore, how to reduce the PT acid content in the oxidation process water is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide an oxidation process water purification system and its usage method, which has the characteristics of reducing the PT acid content in the raffinate and improving product quality.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: an oxidation process water purification system, comprising an extraction tower and a distillation unit, wherein a separation unit is provided between the extraction tower and the distillation unit, the separation unit comprising:

[0007] The cooling crystallization device has its feed end connected to the raffinate discharge end of the extraction tower, and is used to cool, crystallize, and filter the PT acid in the raffinate.

[0008] The heat exchanger has its tube-side feed end connected to the discharge end of the cooling crystallization device, and is used to heat the raffinate.

[0009] The filter, whose inlet end is connected to the tube-side outlet end of the heat exchanger and whose outlet end is connected to the inlet end of the distillation unit, is used to filter residual PT acid crystals.

[0010] Preferably, the cooling crystallization device includes a horizontal tank with an inlet and an outlet. The top of the tank has a cooling water pipe, and one side of the bottom of the tank has a flushing water pipe. The other side, opposite to the flushing water pipe, has a discharge port. A discharge trough is provided at the bottom of the tank. The two ends of the discharge trough along its length are connected to the flushing water pipe and the discharge port, respectively. An upper baffle and a lower baffle are provided in the tank along the flow direction of the raffinate. The lower baffle is located in front of the discharge trough so that the PT acid crystals are blocked by the lower baffle and fall into the discharge trough when they move with the raffinate.

[0011] Preferably, a rotating shaft is provided at the bottom of the tank along the length of the baffle plate. The baffle plate is rotatably connected to the tank via the rotating shaft. One end of the rotating shaft is connected to a turbine. A worm gear and a motor for driving the turbine rotation are provided on the tank.

[0012] Preferably, there are multiple cooling water pipes distributed along the length of the tank, and these multiple cooling water pipes are connected to the main water pipe.

[0013] Preferably, there are multiple flushing water pipes distributed along the length of the tank, and the number and position of the discharge chute, discharge port, and lower baffle plate correspond to the number of flushing water pipes.

[0014] Preferably, the distillation apparatus includes a condenser, the tube side outlet of which is connected to a cooling water pipe and a flushing water pipe, so that cooling water enters from the tube side inlet of the condenser and exits from the tube side outlet of the condenser to the cooling water pipe and the flushing water pipe.

[0015] Preferably, the distillation apparatus includes a reboiler, the shell-side inlet of which is connected to the shell-side outlet of a heat exchanger, so that steam enters the heat exchanger through the shell-side inlet and then enters the shell-side inlet of the reboiler through the shell-side outlet of the heat exchanger.

[0016] Another object of the present invention is to provide a method of using an oxidation process water purification system, comprising the following steps:

[0017] Step 1: The raffinate from the extraction tower enters the cooling crystallization device. Cooling water from the condenser enters the cooling crystallization device through the cooling water pipe. The cooling water cools the raffinate in the cooling crystallization device, and the PT acid in the raffinate crystallizes.

[0018] Step 2: The raffinate exits the cooling and crystallization device and enters the heat exchanger. Steam passes through the heat exchanger and then enters the reboiler to heat the raffinate.

[0019] Step 3: The raffinate exits the heat exchanger and enters the filter to filter out the residual PT acid crystals;

[0020] Step 4: The raffinate passes through the filter and enters the distillation unit for distillation.

[0021] As a preferred embodiment, step one is as follows: the raffinate enters the tank and flows slowly under the obstruction of the upper and lower baffles. After sufficient cooling with the cooling water, the temperature is reduced. After the PT acid crystallizes, the crystals fall into the discharge trough under their own gravity and the obstruction of the lower baffle.

[0022] Preferably, step one also includes: the motor drives the worm gear and turbine to rotate, causing the lower baffle plate to rotate above the discharge trough, and the flushing water pipe is turned on to flush the PT acid crystals in the discharge trough out from the discharge port.

[0023] In summary, the present invention has the following beneficial effects:

[0024] 1. A separation device is installed between the extraction tower and the distillation unit to cool, crystallize, and filter the raffinate exiting the extraction tower, thereby reducing the PT acid content of the raffinate and helping to improve product quality;

[0025] 2. By designing a cooling crystallization device, continuous crystallization of PT acid can be achieved, thereby improving work efficiency;

[0026] 3. When the PT acid crystals in the tank accumulate to a certain extent, the crystals can be discharged during system operation without affecting the normal operation of the system;

[0027] 4. By introducing the condensate and steam from the distillation unit into the cooling crystallization unit, energy recycling is achieved, reducing energy consumption;

[0028] 5. By setting up a heat exchanger, the raffinate can be heated after cooling and crystallization, which facilitates subsequent distillation operations;

[0029] 6. By setting up a filter, the PT acid crystals that escape from the cooling crystallization device are collected, which further reduces the PT acid content and prevents the crystals from entering the subsequent distillation device. Attached Figure Description

[0030] Figure 1 This is a simplified flow chart of the PTA mother liquor extraction process in the background technology;

[0031] Figure 2 This is a simplified process flow diagram of this system;

[0032] Figure 3 This is a front view of the cooling crystallization apparatus;

[0033] Figure 4 This is a side view of the cooling crystallization apparatus;

[0034] Figure 5 This is a top view of the cooling crystallization apparatus;

[0035] Figure 6 This is a sectional view of the inside of the tank;

[0036] Figure 7 This is a sectional view of the side wall of the tank;

[0037] Figure 8 This is a cross-sectional view of the tank from another angle.

[0038] In the diagram, 1. Extraction tower; 2. Distillation unit; 21. Condenser; 22. Reboiler; 23. Distillation tower; 3. Separation unit; 31. Cooling crystallization unit; 311. Tank; 312. Feed inlet; 313. Discharge outlet; 314. Cooling water pipe; 315. Flushing water pipe; 316. Discharge outlet; 317. Discharge trough; 318. Upper baffle plate; 319. Lower baffle plate; 3110. Rotary shaft; 3112. Turbine; 3113. Worm gear; 3114. Motor; 3115. Main water pipe; 32. Heat exchanger; 33. Filter. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings.

[0040] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0041] Example: An oxidation process water purification system

[0042] like Figure 2 As shown, this system includes an extraction tower 1, a separation unit 3, and a distillation unit 2. The separation unit 3 includes a cooling crystallization unit 31, a heat exchanger 32, and a filter 33. The distillation unit 2 includes a distillation tower 23, a condenser 21, and a reboiler 22. The cooling crystallization unit 31 is connected to the condenser 21, and the condensate exiting the condenser 21 enters the cooling crystallization unit 31. The heat exchanger 32 is connected to the reboiler 22, and the steam passes through the heat exchanger 32 before entering the reboiler 22. PX and PTA mother liquors enter the extraction tower 1, where PT acid and benzoic acid are extracted into the PX. The raffinate exiting the extraction tower 1 enters the separation unit 3. After entering the separation unit 3, the raffinate first enters the cooling crystallization unit 31 for cooling and crystallization, then enters the heat exchanger 32 for heating, and then enters the filter 33 to collect the residual PT acid crystals. Finally, the raffinate leaves the filter 33 and enters the distillation unit 2.

[0043] like Figures 3 to 5As shown, the cooling crystallization apparatus 31 includes a horizontal tank 311. The tank 311 is rectangular in shape, with an inlet 312 and an outlet 313 at its two ends along its length. Multiple cooling water pipes 314 are connected to the top of the tank 311. In this embodiment, there are four cooling water pipes 314, evenly distributed along the top of the tank 311, and all four are connected to the same main water pipe 3115. Multiple flushing water pipes 315 are connected to the side of the tank 311. There are also four flushing water pipes 315, which are also connected to the main water pipe 3115. The main water pipe 3115 is connected to the tube-side outlet of the condenser 21 in the distillation apparatus 2, allowing condensate to exit the condenser 21 and enter the tank 311 through the main water pipe 3115 and the cooling water pipes 314, contacting the raffinate and cooling it to crystallize the PT acid. Four discharge ports 316 are connected to the side of the tank body 311 opposite to the flushing water pipe 315, and each discharge port 316 corresponds to each flushing water pipe 315. Valves (not shown in the figure) are installed on the cooling water pipe 314, the flushing water pipe 315 and the discharge ports 316.

[0044] like Figures 6 to 8 As shown, the bottom surface of the tank 311 is provided with several discharge troughs 317, the openings of which are flared. Each discharge trough 317 is connected at both ends to a flushing water pipe 315 and a discharge port 316, respectively, so that the flushing water pipe 315 can flush the PT acid crystals in the discharge trough 317 to the discharge port 316 and discharge them through the discharge port 316. Each tank 311 has several upper baffles 318 and lower baffles 319 distributed along its length. In this embodiment, there are four upper baffles 318 and four lower baffles 319, which are vertically installed at the top and bottom of the tank 311, respectively. Each lower baffle 319 is respectively set at... Figure 6 On the right side of each discharge trough 317. A lower baffle plate 319 is rotatably connected to both side walls of the tank body 311 via a rotating shaft 3110. One end of the rotating shaft 3110 is connected to a turbine 3112. A worm gear 3113, meshing with all the turbines 3112, is installed inside the tank body 311. The worm gear 3113 is connected to a motor 3114. The motor 3114 drives the worm gear 3113 and turbines 3112 to rotate, which in turn drives the rotating shaft 3110 and the lower baffle plate 319 to rotate. When the lower baffle plate 319 rotates downwards, it covers the top of the discharge trough 317.

[0045] How to use:

[0046] Step 1: The raffinate from extraction tower 1 enters the cooling crystallization device 31. Cooling water from condenser 21 enters the cooling crystallization device 31 along cooling water pipe 314. The cooling water cools the raffinate in the cooling crystallization device 31, causing the PT acid in the raffinate to crystallize. Specifically: The raffinate enters the tank 311 through inlet 312 and flows slowly under the obstruction of upper baffle 318 and lower baffle 319. After the raffinate and cooling water have fully interacted, the PT acid crystallizes. The crystals fall into the discharge trough 317 under their own gravity and the obstruction of lower baffle 319. When motor 3114 drives worm gear 3113 and turbine 3112 to rotate in discharge trough 317, the lower baffle 319 rotates to the top of discharge trough 317 and covers it. Then, flushing water pipe 315 is opened to flush the PT acid crystals in discharge trough 317 out through discharge port 316.

[0047] Step 2: The raffinate exits the cooling crystallization device 31 and enters the heat exchanger 32. Steam passes through the heat exchanger 32 and then enters the reboiler 22 to heat the raffinate.

[0048] Step 3: The raffinate exits heat exchanger 32 and enters filter 33 to filter out residual PT acid crystals.

[0049] Step 4: The raffinate exits filter 33 and enters distillation unit 2 for distillation.

Claims

1. An oxidation process water purification system, comprising an extraction tower (1) and a distillation unit (2), characterized in that, A separation device (3) is provided between the extraction tower (1) and the distillation unit (2). The separation device (3) includes: The cooling crystallization device (31) is connected to the raffinate outlet of the extraction tower (1) and is used to cool, crystallize and filter the PT acid in the raffinate. The heat exchanger (32) has its tube-side feed end connected to the discharge end of the cooling crystallization device (31) for heating the raffinate. The filter (33) has its feed end connected to the tube side of the heat exchanger (32) and its discharge end connected to the feed end of the distillation unit (2) for filtering residual PT acid crystals. The cooling crystallization device (31) includes a horizontal tank (311), which has an inlet (312) and an outlet (313). A cooling water pipe (314) is located at the top of the tank (311), and a flushing water pipe (315) is located at the bottom of one side of the tank (311). A discharge port (316) is located on the other side opposite to the flushing water pipe (315). A discharge trough (316) is provided at the bottom of the tank (311). 7) The two ends of the discharge trough (317) along the length direction are connected to the flushing water pipe (315) and the discharge port (316) respectively. The tank body (311) is provided with an upper baffle plate (318) and a lower baffle plate (319) along the flow direction of the raffinate. The lower baffle plate (319) is located in front of the discharge trough (317) so that the PT acid crystals are blocked by the lower baffle plate (319) and fall into the discharge trough (317) when they move with the raffinate. A rotating shaft (3110) is provided at the bottom of the tank (311) along the length of the baffle plate. The baffle plate is rotatably connected to the tank (311) through the rotating shaft (3110). A turbine (3112) is connected to one end of the rotating shaft (3110). A worm (3113) and a motor (3114) are provided on the tank (311) to drive the turbine (3112) to rotate.

2. The oxidation process water purification system according to claim 1, characterized in that, There are multiple cooling water pipes (314) distributed along the length of the tank (311), and the multiple cooling water pipes (314) are connected to the main water pipe (3115).

3. The oxidation process water purification system according to claim 1, characterized in that, There are multiple flushing water pipes (315) distributed along the length of the tank (311). The number and position of the discharge trough (317), discharge port (316), and lower baffle plate (319) correspond to the flushing water pipes (315).

4. The oxidation process water purification system according to claim 1, characterized in that, The distillation apparatus (2) includes a condenser (21). The tube side outlet of the condenser (21) is connected to a cooling water pipe (314) and a flushing water pipe (315), so that the cooling water enters from the tube side inlet of the condenser (21) and exits from the tube side outlet of the condenser (21) to the cooling water pipe (314) and the flushing water pipe (315).

5. The oxidation process water purification system according to claim 1, characterized in that, The distillation unit (2) includes a reboiler (22), the shell-side inlet of the reboiler (22) is connected to the shell-side outlet of the heat exchanger (32), so that steam enters the heat exchanger (32) along the shell-side inlet of the heat exchanger (32) and then enters the shell-side inlet of the reboiler (22) from the shell-side outlet of the heat exchanger (32).

6. The method of using the oxidation process water purification system according to claim 1, characterized in that, Includes the following steps: Step 1: The raffinate from the extraction tower (1) enters the cooling crystallization device (31). The cooling water from the condenser (21) enters the cooling crystallization device (31) along the cooling water pipe (314). The cooling water cools the raffinate in the cooling crystallization device (31), and the PT acid in the raffinate is cooled and crystallized. Step 2: The raffinate exits the cooling crystallization device (31) and enters the heat exchanger (32). Steam passes through the heat exchanger (32) and then enters the reboiler (22) to heat the raffinate. Step 3: The raffinate exits the heat exchanger (32) and enters the filter (33) to filter out the residual PT acid crystals; Step 4: The raffinate exits the filter (33) and enters the distillation unit (2) for distillation.

7. The method of using the oxidation process water purification system according to claim 6, characterized in that, Step one is as follows: the raffinate enters the tank (311) and flows slowly under the obstruction of the upper baffle (318) and the lower baffle (319). After the cooling water is fully discharged, the temperature is reduced. After the PT acid crystallizes, the crystals fall into the discharge tank (317) under the action of their own gravity and the obstruction of the lower baffle (319).

8. The method of using the oxidation process water purification system according to claim 7, characterized in that, Step one also includes: the motor (3114) drives the worm (3113) and turbine (3112) to rotate, so that the lower baffle plate (319) rotates to the top of the discharge trough (317), and the flushing water pipe (315) is turned on to flush out the PT acid crystals in the discharge trough (317) from the discharge port (316).

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