Method for improving oxidation depth of PIA

Abstract

The invention discloses a PIA (isophthalic acid) oxidation depth improving method, and relates to the technical field of manufacturing process reduction by improving the oxidation reaction efficiency of isophthalic acid (PIA) production. By adopting the type of a novel stirrer PHASE JET and changing the mass ratio of cobalt to manganese to bromine in an oxidation reaction catalyst from 1: 1: 2 in the public information to 2.5: 1: 2.2, the product impurity requirement of omitting a hydrogenation refining section in the public patent can be met. A hydrogenation refining section can be omitted, and a secondary deepening reaction system adopted by a certain patent can be omitted, so that the process is further simplified, the energy consumption and the material consumption are reduced, and the production cost and the equipment investment are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of improving the oxidation reaction efficiency of producing isophthalic acid (PIA) to reduce the manufacturing process, and specifically relates to a method for improving the oxidation depth of PIA. Background Art

[0002] The process of manufacturing isophthalic acid, which is a raw material for general bottle-grade polyester chip additives, involves oxidizing and hydrogenating and refining the raw material m-xylene. According to public data, as long as two additional deep oxidation reactors (with operating pressure and temperature higher than the previous oxidation reactor) are connected in series in addition to oxidation in the oxidation process, the hydrogenation and refining process can be omitted. However, increasing the deep reactor with a higher operating temperature will increase the consumption of raw materials such as m-xylene and solvent acetic acid. Now, an improved way of the stirring blades of the oxidation reactor and the mass ratio of the oxidation catalyst cobalt-manganese-bromine is proposed, which can meet the requirements of the impurity content in the product after the secondary deep oxidation reaction in the public information, that is, 3-CBA is 20 - 400 ppm, and the particle size after crystallization is 100 - 130 μm, which is better than 60 - 100 μm in the public information. Summary of the Invention

[0003] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a method for improving the oxidation depth of PIA. By adopting a new type of stirrer PHASE JET in the oxidation reactor and changing the mass ratio of the oxidation reaction catalyst cobalt-manganese-bromine from 1:1:2 in the public information to 2.5:1:2.2, the product impurity requirements for omitting the hydrogenation and refining section in the public patent can be achieved. The PIA production system adopting this method can not only omit the hydrogenation and refining section but also omit the secondary deepening reaction system adopted in a certain patent to further simplify the process, reduce energy consumption and material consumption, and lower production costs and equipment investment.

[0004] To achieve the above object, the present invention is realized through the following technical solutions: A method for improving the oxidation depth of PIA, using m-xylene as a raw material, includes the following steps:

[0005] 1. Oxidation: Feed the m-xylene solution into the oxidation reactor, and carry out a catalytic oxidation reaction with oxygen under the action of a catalyst to generate isophthalic acid and crystallize it to obtain an oxidation slurry; the oxidation reactor is equipped with a stirrer, which generally has two sections of stirring impellers. The lower impeller is of the PITCHED BLADE type with a 45° cross, and the upper impeller is of the DISC TURBINE type. In this method, both sections of impellers are of the same new PHASE JET type, which has better stirring mass transfer and can have a deeper reaction, and there is no need to set up two additional series-connected deep oxidation reactors with higher temperature and pressure.

[0006] 2. Crystallization: Feed the oxidation slurry into the crystallization device for crystallization to obtain a crystallization slurry.

[0007] 3. Filtration: Feed the crystallization slurry into a filtration device for filtration to obtain a PIA cake. Most of the oxidation mother liquor (filtrate) generated by filtration is returned to the oxidation step to participate in the oxidation reaction;

[0008] 4. Drying: Feed the PIA cake into a drying device for drying to obtain a PIA product.

[0009] Preferably, the number of the oxidation reactors is one, which can form the required processing capacity and reaction effect. Its operating temperature is 170 - 190 °C, the operating pressure is 0.8 - 1.2 MPaG, and the residence time of the material is 80 - 110 min.

[0010] The composition and properties of the oxidation slurry can be controlled by controlling the reaction process. For example, preferably, the content of impurity 3 - CBA in the oxidation slurry is 200 - 400 ppm. The particle size after crystallization is 110 - 130 um.

[0011] Preferably, the catalyst is preferably a cobalt - manganese - bromine catalyst, and the mass ratio of cobalt, manganese, and bromine is 2.5:1:2.2. The content of cobalt in the system is 500 - 650 ppm.

[0012] Preferably, in the filtration step, the remaining oxidation mother liquor except for the part returned to the oxidation step can be fed into an oxidation mother liquor treatment device for treatment. The proportion of the oxidation mother liquor fed into the oxidation mother liquor treatment device in all the oxidation mother liquor is 15 - 30%.

[0013] A device for enhancing the oxidation depth of PIA includes an oxidation reactor. The top outlet of the oxidation reactor is connected to a reflux tank for gas - liquid separation after releasing heat through a conveying pipeline successively passing through a washing unit, a first by - product steam heat exchanger, a second by - product steam heat exchanger, a third by - product steam heat exchanger, and a fourth by - product steam heat exchanger.

[0014] Preferably, the top outlet of the reflux drum is sent to the tail gas treatment unit for treatment after passing through the first cooler and the second cooler in sequence through a conveying pipeline to release heat. The conveying pipeline of the bottom outlet of the reflux drum is divided into multiple routes, at least one of which is connected to the solvent dehydration unit for azeotropic distillation dehydration, and one is connected to the top of the washing unit to wash a small amount of meta-xylene, MT acid, etc. in the steam taken out from the top outlet of the oxidation reactor back to the oxidation reactor to participate in the reaction; the conveying pipeline of the dehydrated acid outlet of the solvent dehydration unit is divided into multiple routes, at least one of which is connected to the filtering device as a washing liquid, and one is connected to the washing unit together with the liquid at the bottom of the reflux drum as a washing liquid; the discharge port of the oxidation reactor is connected to the feed port of the first crystallizer, the first crystallizer, the second crystallizer, and the third crystallizer are connected in sequence, the top gas outlets of the second crystallizer and the third crystallizer are connected to the solvent dehydration unit, the discharge port of the third crystallizer is connected to the feed port of the filtering device, the filtrate outlet of the filtering device is connected to the feed port of the oxidation reactor through a mother liquor reflux pipeline, and the filtering device is also connected to the drying device and the oxidation mother liquor treatment device.

[0015] Preferably, the oxidation reactor is used to carry out oxidation reaction of raw materials to obtain oxidation slurry, and is provided with upper and lower sets of PHASE JET type stirring impellers in the oxidation reactor. The oxidation reactor is provided with a feed port, an air inlet, a top outlet, a barrel discharge port and a bottom inlet, wherein the air inlet is connected to an oxygen-containing air source, and the bottom inlet is connected to the bottom discharge port of the washing unit.

[0016] Preferably, the washing unit is provided with a top gas outlet, a top liquid inlet, a bottom gas inlet and a bottom liquid outlet.

[0017] Preferably, the reflux tank is provided with a top outlet and a bottom outlet, which are used to send out the separated gas and liquid respectively.

[0018] Preferably, the solvent dehydration unit is provided with a dehydration acid outlet for sending out the dehydration acid generated after dehydration and a wastewater outlet for sending out the wastewater generated by dehydration.

[0019] Preferably, the filtering device is a rotary pressure filter, and the number can be one, or multiple according to actual needs.

[0020] The beneficial effects of the present invention are as follows: by adopting two groups of PHASE JET continuous stirred tank oxidation reactors and optimizing the catalyst ratio, the reaction yield can be improved while ensuring the purity of the product, eliminating the complicated refining process and its supporting processes, greatly simplifying the process, reducing equipment investment, greatly reducing water consumption and energy consumption, and at the same time significantly reducing the discharge of water pollutants such as sewage and COD. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments;

[0022] Figure 1 It is a schematic structural diagram of Embodiment 1 of the present invention. Specific Embodiments

[0023] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0024] Referring to Figure 1 , the following technical solutions are adopted in this specific embodiment: A method for improving the oxidation depth of PIA, using m-xylene as a raw material, comprising the following steps:

[0025] 1. Oxidation: Feed the m-xylene solution into an oxidation reactor, and carry out a catalytic oxidation reaction with oxygen under the action of a catalyst to generate isophthalic acid and crystallize it to obtain an oxidation slurry; The oxidation reactor is equipped with a stirrer, which generally has two-stage stirring impellers. The lower impeller is of the PITCHED BLADE type with a 45-degree cross, and the upper impeller is of the DISC TURBINE type. In this method, both two-stage impellers are of the same new PHASE JET type, which has better stirring mass transfer and can have a deeper reaction, and there is no need to set up two additional series-connected deep oxidation reactors with higher temperature and pressure.

[0026] 2. Crystallization: Feed the oxidation slurry into a crystallization device for crystallization to obtain a crystallization slurry;

[0027] 3. Filtration: Feed the crystallization slurry into a filtration device for filtration to obtain a PIA filter cake, and most of the oxidation mother liquor (filtrate) generated by filtration is returned to the oxidation step to participate in the oxidation reaction;

[0028] 4. Drying: Feed the PIA filter cake into a drying device for drying to obtain a PIA product.

[0029] It should be noted that the number of the oxidation reactors is one, which can form the required processing capacity and reaction effect. Its operating temperature is 170 - 190 °C, the operating pressure is 0.8 - 1.2 MPaG, and the residence time of the material is 80 - 110 min.

[0030] The composition and properties of the oxidation slurry can be controlled by controlling the reaction process. For example, preferably, the content of the impurity 3-CBA in the oxidation slurry is 200 - 400 ppm. The particle size after crystallization is 110 - 130 um.

[0031] It should be noted that the catalyst is preferably a cobalt-manganese-bromine catalyst, and the mass ratio of cobalt, manganese and bromine is 2.5:1:2.2, and the content of cobalt in the system is 500 - 650 ppm.

[0032] It is worth noting that in the filtration step, the remaining oxidation mother liquor except that returned to the oxidation step can be sent to the oxidation mother liquor treatment device for treatment. The proportion of the oxidation mother liquor sent to the oxidation mother liquor treatment device accounts for 15 to 30% of the total oxidation mother liquor. The remaining oxidation mother liquor can also be treated and / or utilized in other ways.

[0033] A device for increasing the oxidation depth of PIA includes an oxidation reactor 1. The top outlet of the oxidation reactor 1 passes through a washing unit 9, a first byproduct steam heat exchanger 10, a second byproduct steam heat exchanger 11, a third byproduct steam heat exchanger 12 and a fourth byproduct steam heat exchanger 13 through a conveying pipeline in sequence to release heat, and then is connected to a reflux tank 14 for gas-liquid separation to produce corresponding steam for effective heat utilization. The top outlet of the reflux tank 14 passes through a first cooler 15 and a second cooler 16 through a conveying pipeline in sequence to release heat, and then is sent to a tail gas treatment unit 17 for treatment. The conveying pipeline of the bottom outlet of the reflux tank 14 is divided into multiple routes, at least one of which is connected to a solvent dehydration unit 18 for azeotropic distillation dehydration, and one of which is connected to the top of the washing unit 9 to wash a small amount of meta-xylene, MT acid, etc. in the steam taken out of the top outlet of the oxidation reactor 1 together and return it to the oxidation reactor 1 to participate in the reaction; the conveying pipeline of the dehydrated acid outlet of the solvent dehydration unit 18 is divided into multiple routes, at least one of which is connected to a filtering device 7 is used as a washing liquid, and is connected to a washing unit 9 together with the liquid at the bottom of a reflux tank 14 as a washing liquid; the discharge port of the oxidation reactor 1 is connected to the feed port of the first crystallizer 3, the first crystallizer 3, the second crystallizer 4, and the third crystallizer 5 are connected in sequence, the top gas outlets of the second crystallizer 4 and the third crystallizer 5 are connected to the solvent dehydration unit 18, the discharge port of the third crystallizer 5 is connected to the feed port of the filter device 7, the filtrate outlet of the filter device 7 is connected to the feed port of the oxidation reactor 1 through a mother liquor reflux pipe, and the filter device 7 is also connected to a drying device 8 and an oxidation mother liquor treatment device 20.

[0034] It is worth noting that the oxidation reactor is used to carry out oxidation reaction of raw materials to obtain oxidation slurry. The oxidation reactor is provided with upper and lower sets of PHASE JET type stirring impellers. The oxidation reactor is provided with a feed port, an air inlet, a top outlet, a barrel discharge port and a bottom inlet. The air inlet is connected to an oxygen-containing air source, and the bottom inlet is connected to the bottom discharge port of the washing unit.

[0035] It is worth noting that the washing unit 9 is provided with a top gas outlet, a top liquid inlet, a bottom gas inlet, and a bottom liquid outlet, which are used to deliver the separated gas and liquid respectively.

[0036] It should be noted that the crystallization device is used for the crystallization of the oxidation slurry to obtain a crystallization slurry. Its feed port is connected to the discharge port of the oxidation reaction device and consists of one or more crystallizers, preferably 3, including a first crystallizer, a second crystallizer, and a third crystallizer connected in sequence.

[0037] It should be noted that each crystallizer is provided with a feed port, a discharge port, and a top gas outlet. The crystallizers are connected in sequence, and the discharge port of the preceding crystallizer in adjacent crystallizers is connected to the feed port of the succeeding crystallizer. The feed port of the foremost crystallizer constitutes the feed port of the crystallization device, and the bottom outlet of the last crystallizer constitutes the discharge port of the crystallization device; the top gas outlet of the first crystallizer produces the fifth by-product steam through a steam heat exchanger, and the top gas outlets of the second and third crystallizers are connected to the solvent dehydration unit.

[0038] It should be noted that the reflux tank 14 is provided with a top outlet and a bottom outlet, which are respectively used to send out the separated gas and liquid.

[0039] It should be noted that the solvent dehydration unit 18 is provided with a dehydration acid outlet for sending out the dehydration acid generated after dehydration and a waste water outlet for the waste water generated by dehydration.

[0040] It should be noted that the dryer 8 is used for drying the PIA cake to obtain a PIA product, and is provided with a feed port for feeding the PIA cake and a product outlet after drying. The filtering device 7 is preferably a rotary pressure filter, and the number can be one or multiple according to actual needs.

[0041] In addition, the material (cake) transfer between the filter and the dryer can adopt any suitable existing technology, can be connected through a conveyor belt or other conveyor mechanisms, and an intermediate warehouse can be set or not set.

[0042] In the oxidation reactor of this specific embodiment, by adopting the type of the new stirrer PHASE JET and changing the mass ratio of the oxidation reaction catalyst cobalt-manganese-bromine from 1:1:2 in the public information to 2.5:1:2.2, the product impurity requirements of omitting the hydrogenation refining section in the public patent can be achieved. For the PIA production system adopting this method, not only can the hydrogenation refining section be omitted, but also the secondary deepening reaction system adopted in a certain patent can be omitted to further simplify the process, reduce energy consumption and material consumption, and lower production costs and equipment investment.

[0043] Example 1: As Figure 1As shown, air passes through the air compressor unit 2 and is sent into the oxidation reactor 1 as the oxygen-containing gas for the oxidation reaction. In the oxidation reactor 1, with acetic acid as the solvent and cobalt acetate, manganese acetate, and hydrobromic acid as the catalysts, the raw material m-xylene reacts with air under the action of the catalysts to generate PIA. The oxidation reactor 1 is a continuous stirred tank reactor (CSTR) with two sets of PHASE JET type impellers. The operating temperature is 170 - 190 °C, and the operating pressure is 0.8 - 1.2 MPaG. The heat generated by the reaction is carried away from the top of the reactor by the evaporated acetic acid, water, and tail gas. After passing through the washing unit 9 to reduce the solid phase entrainment, a small amount of m-xylene, MT acid, etc. are washed together and returned to the oxidation reactor 1 for reaction. The gas phase at the top of the washing unit 9 successively passes through the first by-product steam heat exchanger 10, the second by-product steam heat exchanger 11, the third by-product steam heat exchanger 12, and the fourth by-product steam heat exchanger 13, is condensed and by-produces steam, and then goes to the reflux tank 14 for gas-liquid separation. The gas at the top outlet of the reflux tank 14 is further cooled by the first cooler (heated by turbine condensate) 15 and the second cooler (circulating water cooler) 16 and then sent to the tail gas treatment unit 17. A small part of the liquid phase (aqueous acetic acid) at the bottom outlet of the reflux tank 14 goes to the solvent dehydration unit 18 for azeotropic distillation dehydration, and most of it returns to the washing unit 9 as the washing liquid to recover the entrained solid phase, a small amount of m-xylene, MT acid, etc. carried out by the oxidation reactor 1 and then returned to the oxidation reactor 1 for further reaction. The acetic acid dehydrated by the solvent dehydration unit 18 is used as the washing liquid for the rotary pressure filter (filter device 7) and the washing unit 9, and the oxidation wastewater is discharged into the sewage treatment station.

[0044] The reaction product (oxidation slurry) is successively sent to the first crystallizer 3, the second crystallizer 4, and the third crystallizer 5 by pressure difference for stepwise cooling, pressure reduction, flashing, and crystallization. The flashed gas at the top of the first crystallizer 3 is condensed by the fifth by-product steam heat exchanger 19 and by-produces steam, and the uncondensed gas enters the tail gas treatment unit 17 to recover acetic acid. The flashed gases of the second crystallizer 4 and the third crystallizer 5 are discharged into the solvent dehydration unit 18 as part of the heat source for the dehydration unit and to recover acetic acid. The slurry at the bottom of the third crystallizer 5 is sent to the rotary pressure filter (filter device 7) by a transfer pump 6. The slurry successively completes three processes in the rotary pressure filter: filtration, multi-pass washing of the filter cake, and blowing drying. After drying, the moisture content of the filter cake can be reduced from 15 - 35% to 10 - 12% or even below 8%. The filter cake is sent to the dryer (drying device 8) for drying and then sent to the storage bin. The filtrate generated by filtration is the oxidation mother liquor. Most of the oxidation mother liquor is returned to the oxidation reactor 1, and the remaining part of the oxidation mother liquor is sent to the oxidation mother liquor treatment device 20 for treatment to recover the useful components therein, and after eliminating the pollution, it is discharged up to standard or reused.

[0045] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for increasing the oxidation depth of PIA, characterized in that: Taking meta-xylene as raw material, the process comprises the following steps: (1) Oxidation: The meta-xylene solution is fed into an oxidation reactor, where it undergoes a catalytic oxidation reaction with oxygen under the action of a catalyst to generate isophthalic acid and crystallize to obtain an oxidized slurry; the oxidation reactor is equipped with an agitator, which generally has two-stage agitating impellers, the lower impeller being a PITCHED BLADE type crossed at 45 degrees, and the upper impeller being a DISC TURBINE type; (2) Crystallization: sending the oxidized slurry into a crystallization device for crystallization to obtain a crystal slurry; (3) Filtration: The crystal slurry is sent to a filtration device for filtration to obtain a PIA filter cake, and most of the oxidation mother liquor produced by filtration is returned to the oxidation step to participate in the oxidation reaction; (4) Drying: The PIA filter cake is sent to a drying device for drying to obtain a PIA product.

2. A method for increasing PIA oxidation depth according to claim 1, characterized in that: The number of the oxidation reactor is one, which can form the required processing capacity and reaction effect; its operating temperature is 170-190°C, the operating pressure is 0.8-1.2MPaG, and the material residence time is 80-110min.

3. A method for increasing PIA oxidation depth according to claim 1, characterized in that: The content of impurity 3-CBA in the oxidation slurry is 200-400 ppm, and the particle size after crystallization is 110-130 um.

4. A method for increasing PIA oxidation depth according to claim 1, characterized in that: The catalyst is a cobalt manganese bromine catalyst, the mass ratio of cobalt manganese bromine is 2.5:1:2.2, and the content of cobalt in the system is 500-650 ppm.

5. A method for increasing PIA oxidation depth according to claim 1, characterized in that: In the filtering step, the remaining oxidation mother liquor except that returned to the oxidation step can be sent to the oxidation mother liquor treatment device for treatment. The proportion of the oxidation mother liquor sent to the oxidation mother liquor treatment device accounts for 15-30% of the total oxidation mother liquor.

6. A PIA oxidation depth enhancement device, characterized in that: The invention comprises an oxidation reactor (1), wherein the top outlet of the oxidation reactor (1) passes through a washing unit (9), a first byproduct steam heat exchanger (10), a second byproduct steam heat exchanger (11), a third byproduct steam heat exchanger (12) and a fourth byproduct steam heat exchanger (13) in sequence through a conveying pipeline to release heat and then is connected to a reflux tank (14) for gas-liquid separation; the top outlet of the reflux tank (14) passes through a first cooler (15) and a second cooler (16) in sequence through a conveying pipeline to release heat and then is sent to a tail gas treatment unit (17) for treatment; the bottom outlet of the reflux tank (14) is divided into a plurality of conveying pipelines, wherein at least one pipeline is connected to a solvent dehydration unit (18) for azeotropic distillation dehydration, and one pipeline is connected to the top of a washing unit (9) to wash a small amount of meta-xylene and MT acid in the steam taken out from the top outlet of the oxidation reactor (1) and return them to the oxidation reactor. The reactor (1) participates in the reaction; the delivery pipeline of the dehydrated acid outlet of the solvent dehydration unit (18) is divided into multiple routes, at least one of which is connected to the filtering device (7) as a washing liquid, and one of which is connected to the washing unit (9) together with the liquid at the bottom of the reflux tank (14) as a washing liquid; the discharge port of the oxidation reactor (1) is connected to the feed port of the first crystallizer (3), the first crystallizer (3), the second crystallizer (4), and the third crystallizer (5) are connected in sequence, the top gas outlets of the second crystallizer (4) and the third crystallizer (5) are connected to the solvent dehydration unit (18), the discharge port of the third crystallizer (5) is connected to the feed port of the filtering device (7), the filtrate outlet of the filtering device (7) is connected to the feed port of the oxidation reactor (1) through the mother liquor reflux pipeline, and the filtering device (7) is also connected to the drying device (8) and the oxidation mother liquor treatment device (20).

7. A PIA oxidation depth improvement device according to claim 6, characterized in that: The oxidation reactor is used to carry out oxidation reaction of raw materials to obtain oxidation slurry. The oxidation reactor is provided with upper and lower sets of PHASE JET type stirring impellers. The oxidation reactor is provided with a feed port, an air inlet, a top outlet, a cylinder discharge port and a bottom inlet. The air inlet is connected to an oxygen-containing air source, and the bottom inlet is connected to the bottom discharge port of the washing unit.

8. A PIA oxidation depth improvement device according to claim 6, characterized in that: The washing unit (9) is provided with a top gas outlet, a top liquid inlet, a bottom gas inlet and a bottom liquid outlet.

9. A PIA oxidation depth improvement device according to claim 6, characterized in that: The reflux tank (14) is provided with a top outlet and a bottom outlet, which are used to send out the separated gas and liquid respectively.

10. A PIA oxidation depth enhancement device according to claim 6, characterized in that: The solvent dehydration unit (18) is provided with a dehydration acid outlet for sending out the dehydration acid generated after dehydration and a wastewater outlet for sending out the wastewater generated by dehydration.

11. A PIA oxidation depth enhancement device according to claim 6, characterized in that: The filtering device (7) adopts a rotary pressure filter.

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