A device and method for extracting m-cyanobenzamide from isophthalonitrile off-spec products

Abstract

This invention provides an apparatus and method for extracting m-cyanobenzamide from substandard isophthalonitrile. The apparatus includes a raw material melting unit, an evaporation unit, and a distillation unit connected in sequence. The evaporation unit includes an evaporator and an evaporation kettle, and the distillation unit includes a distillation column. The lower outlet of the evaporator is connected to the inlet of the evaporation kettle, and the upper outlets of both the evaporator and the evaporation kettle are connected to the distillation column. The m-cyanobenzamide product is collected from the bottom outlet of the distillation column. This invention, through the selection of melting, evaporation, and distillation equipment and related processes, purifies substandard isophthalonitrile. It not only fully recovers m-cyanobenzamide to obtain a high-quality m-cyanobenzamide product but also yields isophthalonitrile, helping to solve the problems of large solid waste volume and high environmental pressure during isophthalonitrile purification, turning waste into treasure and increasing utilization value. The apparatus has a simple structure, can achieve continuous automated operation, has a short production time, and low production cost.

Description

Technical Field

[0001] This invention belongs to the field of organic product refining technology, and relates to an apparatus and method for extracting m-cyanobenzamide from substandard isophthalonitrile products. Background Technology

[0002] Isophthalonitrile, an important aromatic nitrile, is an organic raw material for the synthesis of various chemical products. It can be used to prepare plastics, synthetic fibers, pesticides, and curing agents, and has wide applications in pharmaceuticals, pesticides, and dyes. Isophthalonitrile can be chlorinated to synthesize tetrachloroisophthalonitrile, a product of chlorothalonil, a highly effective and low-toxicity fungicide. Isophthalamide, synthesized through hydrogenation, can be used as a curing agent for epoxy resins and is also a raw material for polyurethane and nylon resins. With the continuous development of downstream products, its application scope and demand are increasing daily, making research on its synthesis and purification processes of great significance.

[0003] Currently, the main method for synthesizing isophthalonitrile is the ammoxidation method, where m-xylene reacts with ammonia and oxygen in the presence of a catalyst to produce isophthalonitrile. However, the isophthalonitrile produced by this method has low purity and a high content of m-cyanobenzamide, making it a substandard product. Substandard isophthalonitrile requires further purification. However, during the purification process, impurities such as m-cyanobenzamide cannot be effectively separated and purified, and can only be treated as solid waste, increasing production costs and posing a significant environmental hazard.

[0004] Currently, the main operations used in the purification of isophthalonitrile include evaporation and distillation. The resulting solid waste contains a high content of intermediate cyanobenzoamide and a large amount of solid waste, which leads to problems such as low isophthalonitrile yield and high purification costs. At the same time, the high amide content also results in more residue in the melter during the downstream chlorothalonil production process, leading to a high content of hexachlorobenzene, an impurity in chlorothalonil products, which is very harmful to the environment and makes it difficult to meet market demand.

[0005] CN 110590603A discloses a continuous distillation purification method for isophthalonitrile. The method involves continuously evaporating and vaporizing molten isophthalonitrile feedstock, followed by distillation of the vaporized isophthalonitrile to obtain purified isophthalonitrile product. This patent purifies crude isophthalonitrile primarily through evaporation and distillation, but its focus is on the purification of isophthalonitrile itself. It does not address the purification of other components, particularly the recovery of amide components such as m-cyanobenzamide. This results in low product yield, high slag discharge, and significant waste.

[0006] CN 111233708A discloses a refining process for isophthalonitrile that ensures safe feeding and smooth slag discharge. The refining process includes: feeding crude isophthalonitrile into a melting reactor using a vacuum feeding method; heating, melting, and evaporating the crude isophthalonitrile to obtain isophthalonitrile vapor; the obtained isophthalonitrile vapor entering a condenser and condensing into liquid isophthalonitrile, which then enters a receiving reactor for heat preservation; after heat preservation, the liquid isophthalonitrile directly enters a slicer for slicing via a liquid level difference, thus completing the refining of isophthalonitrile; the impurities in the crude isophthalonitrile include low-boiling-point impurities and high-boiling-point impurities; the former melts and vaporizes, entering the receiving reactor along with the isophthalonitrile, while the latter remains in the melting reactor to form slag. This refining process also focuses on the refining and purification of isophthalonitrile, but other components are not clearly separated or recovered. Some of them still exist in isophthalonitrile, and others are discharged as residue. In other words, the purification of m-cyanobenzamide is not involved, resulting in low utilization of crude raw materials and serious waste.

[0007] In summary, the refining and purification of substandard isophthalonitrile requires not only the refining of isophthalonitrile itself, but also the purification of other major components such as isocyanobenzamide. This process transforms the solid waste generated during isophthalonitrile purification into valuable resources, increases the utilization value of raw materials and product yield, reduces production costs, and is environmentally friendly. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide an apparatus and method for extracting m-cyanobenzamide from substandard isophthalonitrile. Based on the composition and characteristics of the substandard isophthalonitrile, the apparatus, through the setup of melting, evaporation, and distillation devices and the selection of process conditions, purifies the substandard isophthalonitrile. This not only yields isophthalonitrile but also fully recovers the m-cyanobenzamide, helping to solve the problems of large solid waste volume and high treatment costs during the isophthalonitrile purification process. It transforms waste into valuable resources, increases product yield, and reduces production costs.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] On one hand, the present invention provides an apparatus for extracting m-cyanobenzamide from substandard isophthalonitrile. The apparatus includes a raw material melting unit, an evaporation unit, and a distillation unit connected in sequence. The evaporation unit includes an evaporator and an evaporation kettle, and the distillation unit includes a distillation column. The lower outlet of the evaporator is connected to the inlet of the evaporation kettle, and the upper outlets of both the evaporator and the evaporation kettle are connected to the inlet of the distillation column. The bottom outlet of the distillation column yields the m-cyanobenzamide product.

[0011] In this invention, the composition of the non-conforming isophthalonitrile is relatively complex, especially with a high amide content. Besides recovering the isophthalonitrile, it also needs to be purified to obtain high-purity m-cyanobenzamide. Based on the characteristics of the non-conforming isophthalonitrile, a melting unit is first set up to form a liquid phase material. Then, through a two-stage evaporation unit, isophthalonitrile and m-cyanobenzamide are fully evaporated and vaporized. Finally, a distillation column is used to separate the two, yielding high-purity isophthalonitrile and m-cyanobenzamide products. The product yield is high, and solid waste is low. The device has a simple structure, strong operational continuity, and a high degree of automation, which helps reduce production costs and environmental pressure.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0013] As a preferred technical solution of the present invention, the raw material melting unit includes a melting kettle, the melting kettle is provided with a stirring assembly inside and a jacket outside, and heat transfer oil is introduced into the jacket for heating.

[0014] Preferably, a buffer tank is provided between the raw material melting unit and the evaporation unit, the lower outlet of the melting kettle is connected to the inlet of the buffer tank, and the lower outlet of the buffer tank is connected to the inlet of the evaporator.

[0015] Preferably, the buffer tank is also provided with a jacket on the outside, and heat transfer oil is circulated into the jacket for heat tracing.

[0016] Preferably, a first delivery pump is provided between the melting vessel and the buffer tank, and the first delivery pump is a metering pump.

[0017] In this invention, the non-conforming isophthalonitrile is continuously discharged after melting, and can be metered under negative pressure or mechanically metered. The former is further limited to automatic metering and extraction under negative pressure.

[0018] As a preferred technical solution of the present invention, the evaporator is a vacuum evaporator, including any one of a shell-and-tube evaporator, a rising film evaporator, a falling film evaporator, or a scraped evaporator.

[0019] Preferably, the evaporator is equipped with a stirring assembly inside and a jacket on the outside.

[0020] Preferably, the heating medium for the evaporator and evaporator kettle includes heat transfer oil.

[0021] Preferably, the bottom outlet of the evaporator is also connected to a slag discharge tank.

[0022] Preferably, a second conveying pump is also provided between the evaporation kettle and the slag discharge tank.

[0023] Preferably, the bottom outlet of the slag discharge tank is sequentially connected to a solid waste slicer and a solid waste conveyor.

[0024] In this invention, a certain liquid level is maintained in the evaporation kettle, and the liquid level is automatically controlled by the outlet pump of the evaporation kettle.

[0025] As a preferred technical solution of the present invention, the distillation column includes a packed distillation column or a plate distillation column, preferably a packed distillation column.

[0026] Preferably, the distillation column is provided with a top condenser and a bottom reboiler.

[0027] Preferably, both the top condenser and the bottom reboiler use heat transfer oil as the heat exchange medium.

[0028] Preferably, the bottom outlet of the distillation column is also connected to a product receiving tank.

[0029] Preferably, a third transfer pump is also provided between the distillation column and the product receiving tank.

[0030] Preferably, the bottom outlet of the product receiving tank is sequentially connected to a product slicer, a product conveyor, and a product packaging machine.

[0031] In this invention, the isophthalonitrile and m-cyanobenzamide gases generated during the evaporation process are continuously fed into a distillation column for purification. The isophthalonitrile product can be continuously collected from the upper part of the distillation column, and a high-content m-cyanobenzamide product is obtained from the bottom of the distillation column.

[0032] As a preferred embodiment of the present invention, the upper liquid phase outlet of the distillation column is also connected to an isophthalonitrile receiving tank.

[0033] Preferably, the outlet of the top condenser at the top of the distillation column is further connected in sequence to a tail gas condenser and a tail gas trap.

[0034] Preferably, the bottom outlet of the exhaust gas condenser is connected to the inlet of the isophthalonitrile receiving tank.

[0035] Preferably, the heat exchange medium of the exhaust gas condenser includes heat transfer oil.

[0036] Preferably, the bottom outlet of the exhaust gas collector is connected to a buffer chamber.

[0037] Preferably, the heat exchange medium of the exhaust gas trap includes circulating water or chilled water.

[0038] In this invention, the inlet and outlet of the buffer chamber are equipped with shut-off valves to facilitate the buffering and centralized discharge of continuously collected materials.

[0039] On the other hand, the present invention provides a method for extracting m-cyanobenzamide using the above-described apparatus, the method comprising the following steps:

[0040] (1) After melting the substandard isophthalonitrile, it is evaporated in two stages. The liquid remaining after the first stage of evaporation is evaporated in the second stage. Both the first and second stages of evaporation generate gas. The remaining material after the second stage of evaporation is discharged.

[0041] (2) The gas obtained from evaporation in step (1) is purified by distillation to obtain the m-cyanobenzamide product.

[0042] As a preferred technical solution of the present invention, the content of the non-conforming isophthalonitrile in step (1) is 50-90 wt%, such as 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, or 90 wt%, but not limited to the listed values; other unlisted values ​​within this range are also applicable. The content of m-cyanobenzoamide is 0.01-40 wt%, such as 0.01 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] Preferably, the non-conforming isophthalonitrile product described in step (1) is first added to a melting kettle for melting, and then transported to a buffer tank.

[0044] Preferably, the melting temperature of the non-conforming isophthalonitrile is 160–260°C, such as 160°C, 170°C, 180°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or 260°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 180–240°C being the preferred value.

[0045] Preferably, the heating medium used in the melting vessel and the buffer tank includes heat transfer oil.

[0046] Preferably, the temperature of the heat transfer oil is 180 to 300°C, such as 180°C, 200°C, 220°C, 240°C, 250°C, 260°C, 280°C, or 300°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] Preferably, the substandard isophthalonitrile is melted and discharged by pumping, and is quantitatively delivered by a metering pump.

[0048] As a preferred technical solution of the present invention, the two-stage evaporation in step (1) is carried out in an evaporator and an evaporation kettle respectively. The first-stage evaporation includes heating and vaporizing part of the isophthalonitrile and part of the isocyanobenzoamide in the evaporator. The second-stage evaporation includes continuing to evaporate and vaporize the remaining high-boiling substances and unvaporized isophthalonitrile in the evaporation kettle. Finally, the remaining high-boiling substances are discharged from the bottom of the evaporation kettle.

[0049] In this invention, the components vaporized in the evaporator include a portion of isophthalonitrile and a portion of isocyanobenzamide.

[0050] Preferably, the temperature of the gas phase after heating and vaporization in the evaporator is 160-250°C, such as 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the temperature of the liquid phase in the evaporator is 200-300℃, such as 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃ or 300℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 240-280℃.

[0052] Preferably, the vacuum degree in the evaporator and the evaporating kettle is independently 55 to 99 kPa, such as 55 kPa, 60 kPa, 65 kPa, 70 kPa, 75 kPa, 80 kPa, 85 kPa, 90 kPa, 95 kPa or 99 kPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 85 to 95 kPa.

[0053] Preferably, the evaporator and evaporation kettle are heated using heat transfer oil.

[0054] Preferably, the temperature of the heat transfer oil is 220-340°C, such as 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 300°C, 320°C, or 340°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 240-320°C being the preferred value.

[0055] Preferably, the high-boiling-point substance includes terephthalonitrile, m-cyanobenzonitrile, and benzonitrile.

[0056] Preferably, the high-boiling-point substance is fed into a slag discharge tank via a second transfer pump, and then packaged after cooling and slicing.

[0057] As a preferred technical solution of the present invention, the vapor obtained by evaporation in step (2) enters the distillation column for distillation, the bottom of the distillation column is taken out as m-cyanobenzamide product, and the top of the distillation column is taken out as m-phthalonitrile.

[0058] Preferably, the feed to the distillation column is a bubble-point feed.

[0059] Preferably, the top temperature of the distillation column is 160-250°C, such as 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 160-200°C being the preferred value.

[0060] Preferably, the bottom temperature of the distillation column is 200-300℃, such as 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃ or 300℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 250-280℃ being the preferred value.

[0061] Preferably, the vacuum degree of the distillation column is 55-99 kPa, such as 55 kPa, 60 kPa, 65 kPa, 70 kPa, 75 kPa, 80 kPa, 85 kPa, 90 kPa, 95 kPa or 99 kPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 85-98 kPa.

[0062] Preferably, the bottom liquid level of the distillation column is 0 to 3000 mm, such as 2 mm, 200 mm, 400 mm, 600 mm, 800 mm, 1000 mm, 1200 mm, 1500 mm, 1600 mm, 1800 mm, 2000 mm, 2200 mm, 2500 mm, 2800 mm or 3000 mm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0063] In this invention, the reboiler of the distillation column is part of the distillation column structure, and the liquid level in the reboiler is the bottom liquid level of the distillation column. At the same time, since the reboiler is connected to the reboiler, it is also the liquid level of the reboiler. The evaporation rate of the reboiler is ensured by controlling the liquid level. The liquid level of the cyanobenzamide product in the middle of the reboiler is stable, and its liquid level is automatically controlled by the product discharge pump.

[0064] Preferably, the top condenser and bottom reboiler of the distillation column both use heat transfer oil for heat exchange.

[0065] Preferably, the feed temperature of the heat transfer oil in the top condenser of the tower is 150-240°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C or 240°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 160-220°C.

[0066] Preferably, the feed temperature of the heat transfer oil in the reboiler at the bottom of the tower is 220-340°C, such as 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 300°C, 320°C, or 340°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 220-300°C being the preferred value.

[0067] Preferably, the bottom liquid product of the distillation column is sent to the product receiving tank by a third transfer pump, and then cooled, sliced ​​and packaged by a product slicer.

[0068] Preferably, the purity of the m-cyanobenzamide product is 80-99 wt%, such as 80 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, or 99 wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 90-98 wt% being the preferred value.

[0069] As a preferred technical solution of the present invention, the top material of the distillation column is condensed, and part of the condensate is collected into the isophthalonitrile receiving tank to obtain the byproduct isophthalonitrile, and part of it is refluxed for further distillation.

[0070] Preferably, the reflux ratio of the distillation column is 0.5 to 5, such as 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] Preferably, the uncondensed gas at the top of the distillation column passes through a tail gas condenser, the condensate is returned to the isophthalonitrile receiving tank, and the non-condensable components are recovered by the tail gas trap.

[0072] Preferably, the exhaust gas condenser is cooled by heat transfer oil, and the inlet temperature of the heat transfer oil is 140-230°C, such as 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C or 230°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0073] Preferably, the exhaust gas collector is cooled by circulating water or chilled water, and the inlet temperature of the circulating water or chilled water is 1 to 50°C, such as 1°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 7 to 30°C.

[0074] Preferably, the byproduct captured by the exhaust gas collector is isophthalonitrile solid, which is packaged after passing through a buffer chamber.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] (1) Based on the composition and characteristics of unqualified isophthalonitrile, this invention purifies unqualified isophthalonitrile by setting up melting, evaporation, distillation and other devices and selecting related process operations. It can not only obtain isophthalonitrile, but also fully recover m-cyanobenzamide to obtain high-quality m-cyanobenzamide products with a purity of over 80%, and further optimization can reach over 90%. The product yield is high, which helps to solve the problems of large amount of solid waste, high environmental pressure and high treatment cost in the purification process of isophthalonitrile. It turns solid waste into treasure and improves the utilization value of the product.

[0077] (2) The device described in this invention has a simple structure, strong operation continuity, and a wide range of applicable raw materials. It can realize continuous automated operation of the entire production process, greatly shortening the production time and reducing the production cost. Attached Figure Description

[0078] Figure 1 This is a schematic diagram of the apparatus for extracting m-cyanobenzamide from non-conforming isophthalonitrile products provided in Embodiment 1 of the present invention;

[0079] Among them, 1-melting kettle, 2-first transfer pump, 3-buffer tank, 4-evaporator, 5-evaporation kettle, 6-second transfer pump, 7-slag discharge tank, 8-solid waste slicer, 9-solid waste conveyor, 10-distillation column, 11-top condenser, 12-bottom reboiler, 13-third transfer pump, 14-product receiving tank, 15-product slicer, 16-product conveyor, 17-product packaging machine, 18-isophthalonitrile receiving tank, 19-tail gas condenser, 20-tail gas trap, 21-buffer silo. Detailed Implementation

[0080] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0081] The following are typical but non-limiting embodiments of the present invention:

[0082] Example 1:

[0083] This embodiment provides an apparatus for extracting m-cyanobenzamide from non-compliant isophthalonitrile products. A schematic diagram of the apparatus is shown below. Figure 1 As shown, it includes a raw material melting unit, an evaporation unit, and a distillation unit connected in sequence. The evaporation unit includes an evaporator 4 and an evaporation kettle 5. The distillation unit includes a distillation column 10. The lower outlet of the evaporator 4 is connected to the inlet of the evaporation kettle 5. The upper outlets of the evaporator 4 and the evaporation kettle 5 are both connected to the inlet of the distillation column 10. The bottom outlet of the distillation column 10 produces m-cyanobenzamide.

[0084] The raw material melting unit includes a melting kettle 1, which has a stirring assembly inside and a jacket on the outside. Heat transfer oil is circulated through the jacket for heating.

[0085] A buffer tank 3 is also provided between the raw material melting unit and the evaporation unit. The lower outlet of the melting kettle 1 is connected to the inlet of the buffer tank 3, and the lower outlet of the buffer tank 3 is connected to the inlet of the evaporator 4.

[0086] The buffer tank 3 is also provided with a jacket on the outside, and heat transfer oil is circulated into the jacket for heat tracing.

[0087] A first delivery pump 2 is also provided between the melting kettle 1 and the buffer tank 2. The first delivery pump 2 is a metering pump.

[0088] The evaporator 4 is a vacuum evaporator, specifically a falling film evaporator.

[0089] The evaporator 5 is equipped with a stirring assembly inside and a jacket on the outside.

[0090] The bottom outlet of the evaporator 5 is also connected to a slag discharge tank 7.

[0091] A second conveying pump 6 is also provided between the evaporation kettle 5 and the slag discharge tank 7. The bottom outlet of the slag discharge tank 7 is connected in sequence to a solid waste slicer 8 and a solid waste conveyor 9.

[0092] The distillation column 10 is a packed distillation column.

[0093] The distillation column 10 is equipped with a top condenser 11 at the top and a bottom reboiler 12 at the bottom.

[0094] Both the top condenser 11 and the bottom reboiler 12 of the tower use heat transfer oil as the heat exchange medium.

[0095] The bottom outlet of the distillation column 10 is also connected to a product receiving tank 14.

[0096] A third transfer pump 13 is also provided between the distillation column 10 and the product receiving tank 14.

[0097] The bottom outlet of the product receiving tank 14 is sequentially connected to a product slicer 15, a product conveyor 16, and a product packaging machine 17.

[0098] The upper liquid phase outlet of the distillation column 10 is also connected to an isophthalonitrile receiving tank 18.

[0099] The outlet of the top condenser 11 at the top of the distillation column 10 is also connected in sequence to a tail gas condenser 19 and a tail gas collector 20.

[0100] The bottom outlet of the exhaust gas condenser 19 is connected to the inlet of the isophthalonitrile receiving tank 18.

[0101] The heat exchange medium of the exhaust gas condenser 19 is heat transfer oil.

[0102] The bottom outlet of the exhaust gas collector 20 is connected to a buffer chamber 21.

[0103] The heat exchange medium of the exhaust gas collector 20 is circulating water.

[0104] Example 2:

[0105] This embodiment provides an apparatus for extracting m-cyanobenzamide from non-conforming isophthalonitrile. The apparatus includes a raw material melting unit, an evaporation unit, and a distillation unit connected in sequence. The evaporation unit includes an evaporator 4 and an evaporation kettle 5. The distillation unit includes a distillation column 10. The lower outlet of the evaporator 4 is connected to the inlet of the evaporation kettle 5. The upper outlets of both the evaporator 4 and the evaporation kettle 5 are connected to the inlet of the distillation column 10. The bottom outlet of the distillation column 10 yields the m-cyanobenzamide product.

[0106] The raw material melting unit includes a melting kettle 1, which has a stirring assembly inside and a jacket on the outside. Heat transfer oil is circulated through the jacket for heating.

[0107] A buffer tank 3 is also provided between the raw material melting unit and the evaporation unit. The lower outlet of the melting kettle 1 is connected to the inlet of the buffer tank 3, and the lower outlet of the buffer tank 3 is connected to the inlet of the evaporator 4.

[0108] The buffer tank 3 is also provided with a jacket on the outside, and heat transfer oil is circulated into the jacket for heat tracing.

[0109] A first delivery pump 2 is also provided between the melting kettle 1 and the buffer tank 2. The first delivery pump 2 is a metering pump.

[0110] The evaporator 4 is a vacuum evaporator, specifically a scraped evaporator.

[0111] The evaporator 5 is equipped with a stirring assembly inside and a jacket on the outside.

[0112] The bottom outlet of the evaporator 5 is also connected to a slag discharge tank 7.

[0113] A second conveying pump 6 is also provided between the evaporation kettle 5 and the slag discharge tank 7. The bottom outlet of the slag discharge tank 7 is connected in sequence to a solid waste slicer 8 and a solid waste conveyor 9.

[0114] The distillation column 10 is a plate distillation column.

[0115] The distillation column 10 is equipped with a top condenser 11 at the top and a bottom reboiler 12 at the bottom.

[0116] Both the top condenser 11 and the bottom reboiler 12 of the tower use heat transfer oil as the heat exchange medium.

[0117] The bottom outlet of the distillation column 10 is also connected to a product receiving tank 14.

[0118] A third transfer pump 13 is also provided between the distillation column 10 and the product receiving tank 14.

[0119] The bottom outlet of the product receiving tank 14 is sequentially connected to a product slicer 15, a product conveyor 16, and a product packaging machine 17.

[0120] The upper liquid phase outlet of the distillation column 10 is also connected to an isophthalonitrile receiving tank 18.

[0121] The outlet of the top condenser 11 at the top of the distillation column 10 is also connected to a tail gas trap 20.

[0122] The bottom outlet of the exhaust gas collector 20 is connected to a buffer chamber 21.

[0123] The heat exchange medium of the exhaust gas collector 20 is chilled water.

[0124] Example 3:

[0125] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile products. The method is carried out using the apparatus in Example 1 and includes the following steps:

[0126] (1) The unqualified isophthalonitrile is first added to the melting kettle 1 for melting. The unqualified isophthalonitrile has an isophthalonitrile content of 80wt% and an isocyanobenzamide content of 15wt%. The melting temperature is 190℃ and the heating medium is heat transfer oil at 240℃. The melted material is then quantitatively transported to the buffer tank 3 by a metering pump. The liquid level in the melting kettle 1 is maintained at 1800mm.

[0127] The molten material is then subjected to primary and secondary evaporation in evaporator 4 and evaporation kettle 5, respectively. The primary evaporation involves heating and vaporizing a portion of isophthalonitrile and a portion of isocyanobenzoamide in the evaporator 4. The temperature of the vapor phase after vaporization in evaporator 4 is 210°C and the vacuum degree is 90 kPa. The secondary evaporation involves further evaporation and vaporization of the remaining high-boiling-point substances and unvaporized unqualified isophthalonitrile in evaporation kettle 5. The temperature of the liquid phase in evaporation kettle 5 is 240°C and the vacuum degree is 90 kPa. The liquid level in evaporation kettle 5 is maintained at 1200 mm. Evaporator 4 and evaporation kettle 5 are heated with heat transfer oil at 260°C. Finally, the remaining high-boiling-point substances are discharged from the bottom of evaporation kettle 5 and sent to slag discharge tank 7 by the second transfer pump 6. After cooling and slicing, the material is packaged.

[0128] (2) In step (1), the vapors obtained from the two-stage evaporation are both fed into the distillation column 10 for distillation. The feed of the distillation column 10 is bubble point feed, the top temperature of the column is 180℃, the vacuum degree is 95kPa, and the reflux ratio is 1.8. The top material is condensed by the top condenser 11. Part of the condensate is collected and enters the isophthalonitrile receiving tank 18 to obtain isophthalonitrile product. Part of it is refluxed for distillation again. The top condenser 11 uses heat transfer oil for heat exchange. The feed temperature of the heat transfer oil is 165℃. The uncondensed vapors at the top of the column pass through the tail gas condenser 19. The condensate is returned to the isophthalonitrile receiving tank 18. The non-condensable components enter the tail gas collector 20 for recovery. The tail gas condenser 19 is cooled by heat transfer oil. The inlet temperature of the heat transfer oil is 160℃. The tail gas collector 20 is cooled by circulating water. The inlet temperature of the circulating water is 20℃. The components collected by the tail gas collector 20 are packaged after passing through the buffer tank 21.

[0129] The bottom temperature of the distillation column 10 is 280℃, the vacuum degree is 85kPa, the bottom liquid level of the distillation column 10 is maintained at 1600mm, the bottom reboiler 12 uses heat transfer oil for heat exchange, and the feed temperature of the heat transfer oil is 300℃; the m-cyanobenzamide product is collected from the bottom of the distillation column 10 and sent to the product receiving tank 14 through the third transfer pump 13, and then cooled, sliced ​​and packaged by the product slicer 15.

[0130] In this embodiment, the above method is used to purify the substandard isophthalonitrile product, and the resulting m-cyanobenzamide product has a high quality and its purity can reach 93%.

[0131] Example 4:

[0132] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile. The method is the same as that in Example 3, except that the reflux ratio in step (2) is 2 and the bottom temperature of the distillation column 10 is 240°C.

[0133] In this embodiment, the above method is used to purify the substandard isophthalonitrile product, and the resulting m-cyanobenzamide product has a high quality and its purity can reach 85%.

[0134] Example 5:

[0135] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile products. The method is the same as that in Example 3, except that the vacuum degree at the top of the column in step (2) is 98 kPa and the reflux ratio is 2.

[0136] In this embodiment, the above method is used to purify the substandard isophthalonitrile product, and the resulting m-cyanobenzamide product has a high quality and its purity can reach 95%.

[0137] Example 6:

[0138] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile. The method is the same as that in Example 3, except that the reflux ratio in step (2) is 2.5 and the bottom temperature of the distillation column 10 is 230°C.

[0139] In this embodiment, the purification of non-conforming isophthalonitrile products using the above method can achieve a purity of 80% for the obtained isophthalonitrile product and a purity of over 99% for the isophthalonitrile by-product.

[0140] Example 7:

[0141] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile. The method is the same as that in Example 3, except that the vacuum degree of evaporator 4 and evaporator 5 in step (1) is 95 kPa, and the vacuum degree of the bottom of distillation column 10 is 95 kPa.

[0142] In this embodiment, the above method is used to purify the substandard isophthalonitrile product, and the resulting m-cyanobenzamide product has a high quality and its purity can reach 90%.

[0143] Example 8:

[0144] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile products. The method is carried out using the apparatus in Example 1 and includes the following steps:

[0145] (1) The unqualified isophthalonitrile is first added to the melting kettle 1 for melting. The unqualified isophthalonitrile has an isophthalonitrile content of 50wt% and an isocyanobenzoamide content of 40wt%. The melting temperature is 250℃ and the heating medium is heat transfer oil at 300℃. The melted material is then quantitatively transported to the buffer tank 3 by a metering pump. The liquid level in the melting kettle 1 is maintained at 600mm.

[0146] The molten material is then subjected to primary and secondary evaporation in evaporator 4 and evaporation kettle 5, respectively. The primary evaporation involves heating and vaporizing a portion of isophthalonitrile and a portion of isocyanobenzoamide in the evaporator 4. The temperature of the vapor phase after vaporization in evaporator 4 is 240°C and the vacuum degree is 60 kPa. The secondary evaporation involves further evaporation and vaporization of the remaining high-boiling-point substances and unvaporized unqualified isophthalonitrile in evaporation kettle 5. The temperature of the liquid phase in evaporation kettle 5 is 280°C and the vacuum degree is 60 kPa. The liquid level in evaporation kettle 5 is maintained at 800 mm. Evaporator 4 and evaporation kettle 5 are heated with heat transfer oil at 300°C. Finally, the remaining high-boiling-point substances are discharged from the bottom of evaporation kettle 5 and sent to slag discharge tank 7 by the second transfer pump 6. After cooling and slicing, the material is packaged.

[0147] (2) In step (1), the vapors obtained from the two-stage evaporation are both fed into the distillation column 10 for distillation. The feed of the distillation column 10 is bubble point feed, the top temperature of the column is 230℃, the vacuum degree is 65kPa, and the reflux ratio is 1.5. The top material is condensed by the top condenser 11. Part of the condensate is collected and enters the isophthalonitrile receiving tank 18 to obtain isophthalonitrile product. Part of it is refluxed for distillation again. The top condenser 11 uses heat transfer oil for heat exchange. The feed temperature of the heat transfer oil is 200℃. The uncondensed vapors at the top of the column pass through the tail gas condenser 19. The condensate is returned to the isophthalonitrile receiving tank 18. The non-condensable components enter the tail gas collector 20 for recovery. The tail gas condenser 19 is cooled by heat transfer oil. The inlet temperature of the heat transfer oil is 190℃. The tail gas collector 20 is cooled by circulating water. The inlet temperature of the circulating water is 10℃. The components collected by the tail gas collector 20 are packaged after passing through the buffer tank 21.

[0148] The bottom temperature of the distillation column 10 is 300℃, the vacuum degree is 62kPa, the bottom liquid level of the distillation column 10 is maintained at 900mm, the bottom reboiler 12 uses heat transfer oil for heat exchange, and the feed temperature of the heat transfer oil is 340℃; the m-cyanobenzamide product is collected from the bottom of the distillation column 10 and sent to the product receiving tank 14 through the third transfer pump 13, and then cooled, sliced ​​and packaged by the product slicer 15.

[0149] In this embodiment, the above method is used to purify the substandard isophthalonitrile product, and the resulting m-cyanobenzamide product has a high quality and its purity can reach 92%.

[0150] Example 9:

[0151] This embodiment provides a method for extracting m-cyanobenzamide from non-conforming isophthalonitrile products. The method is carried out using the apparatus in Example 1 and includes the following steps:

[0152] (1) The unqualified isophthalonitrile is first added to the melting kettle 1 for melting. The unqualified isophthalonitrile has an isophthalonitrile content of 90wt% and an isocyanobenzoamide content of 2wt%. The melting temperature is 170℃ and the heating medium is heat transfer oil at 200℃. The melted material is then quantitatively transported to the buffer tank 3 by a metering pump. The liquid level in the melting kettle 1 is maintained at 2000mm.

[0153] The molten material is then subjected to primary and secondary evaporation in evaporator 4 and evaporation kettle 5, respectively. The primary evaporation involves heating and vaporizing a portion of isophthalonitrile and a portion of isocyanobenzoamide in the evaporator 4. The temperature of the vapor phase after vaporization in evaporator 4 is 200°C and the vacuum degree is 90 kPa. The secondary evaporation involves further evaporation and vaporization of the remaining high-boiling-point substances and unvaporized unqualified isophthalonitrile in evaporation kettle 5. The temperature of the liquid phase in evaporation kettle 5 is 210°C and the vacuum degree is 90 kPa. The liquid level in evaporation kettle 5 is maintained at 1200 mm. Evaporator 4 and evaporation kettle 5 are heated with heat transfer oil at 280°C. Finally, the remaining high-boiling-point substances are discharged from the bottom of evaporation kettle 5 and sent to slag discharge tank 7 by the second transfer pump 6. After cooling and slicing, the material is packaged.

[0154] (2) In step (1), the vapors obtained from the two-stage evaporation are both fed into the distillation column 10 for distillation. The feed of the distillation column 10 is bubble point feed, the top temperature of the column is 175℃, the vacuum degree is 95kPa, and the reflux ratio is 1.0. The top material is condensed by the top condenser 11. Part of the condensate is collected and enters the isophthalonitrile receiving tank 18 to obtain isophthalonitrile product. Part of it is refluxed for distillation again. The top condenser 11 uses heat transfer oil for heat exchange. The feed temperature of the heat transfer oil is 165℃. The uncondensed vapors at the top of the column pass through the tail gas condenser 19. The condensate is returned to the isophthalonitrile receiving tank 18. The non-condensable components enter the tail gas collector 20 for recovery. The tail gas condenser 19 is cooled by heat transfer oil. The inlet temperature of the heat transfer oil is 160℃. The tail gas collector 20 is cooled by circulating water. The inlet temperature of the circulating water is 5℃. The components collected by the tail gas collector 20 are packaged after passing through the buffer tank 21.

[0155] The bottom temperature of the distillation column 10 is 240℃, the vacuum degree is 90kPa, the bottom liquid level of the distillation column 10 is maintained at 2800mm, the reboiler 12 at the bottom of the column uses heat transfer oil for heat exchange, and the feed temperature of the heat transfer oil is 280℃; the m-cyanobenzamide product is collected from the bottom of the distillation column 10 and sent to the product receiving tank 14 through the third transfer pump 13, and then cooled, sliced ​​and packaged by the product slicer 15.

[0156] In this embodiment, the above method is used to purify the non-conforming isophthalonitrile product, and the purity of the obtained isocyanobenzamide product can reach 81%, and the purity of the by-product isophthalonitrile can reach 98%.

[0157] As can be seen from the above embodiments, this invention, based on the composition and characteristics of unqualified isophthalonitrile, purifies the unqualified isophthalonitrile by setting up melting, evaporation, and distillation devices and selecting related process operations. This not only yields isophthalonitrile but also fully recovers m-cyanobenzamide, resulting in a high-quality m-cyanobenzamide product with a purity of over 80%, and further optimization can achieve over 90%. The high product yield helps solve the problems of large solid waste volume, high environmental pressure, and high treatment costs during the isophthalonitrile purification process, turning solid waste into valuable resources and improving product utilization value. The device has a simple structure, strong operational continuity, and a wide range of applicable raw materials, enabling continuous automated operation throughout the entire production process, greatly shortening production time and reducing production costs.

[0158] The applicant declares that the present invention is illustrated through the above embodiments with detailed apparatus and methods, but the present invention is not limited to the above detailed apparatus and methods, that is, it does not mean that the present invention must rely on the above detailed apparatus and methods to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the apparatus of the present invention, additions of auxiliary devices, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An apparatus for extracting m-cyanobenzamide from isophthalonitrile off-specification product, characterized by, The apparatus includes a raw material melting unit, an evaporation unit, and a distillation unit connected in sequence. The evaporation unit includes an evaporator and an evaporation kettle, and the distillation unit includes a distillation column. The lower outlet of the evaporator is connected to the inlet of the evaporation kettle, and the upper outlets of both the evaporator and the evaporation kettle are connected to the inlet of the distillation column. The bottom outlet of the distillation column is connected to a product receiving tank for collecting the m-cyanobenzamide product. The non-conforming isophthalonitrile product contains 50-90 wt% isophthalonitrile and 0.01-40 wt% isocyanobenzoamide. The two-stage evaporation is carried out in an evaporator and an evaporation kettle, respectively. The first-stage evaporation includes heating and vaporizing part of the isophthalonitrile and part of the isocyanobenzamide in the evaporator. The second-stage evaporation includes the continued evaporation and vaporization of the remaining high-boiling-point substances and the unvaporized isophthalonitrile non-conforming products in the evaporation kettle. Finally, the remaining high-boiling-point substances are discharged from the bottom of the evaporation kettle. The distillation column is equipped with a top condenser and a bottom reboiler; the upper liquid phase outlet of the distillation column is connected to an isophthalonitrile receiving tank; the outlet of the top condenser at the top of the distillation column is also connected in sequence to a tail gas condenser and a tail gas trap; the bottom outlet of the tail gas condenser is connected to the inlet of the isophthalonitrile receiving tank.

2. The apparatus according to claim 1, characterized in that, The raw material melting unit includes a melting kettle, which has a stirring assembly inside and a jacket on the outside. Heat transfer oil is circulated through the jacket for heating.

3. The apparatus according to claim 2, characterized in that, A buffer tank is also provided between the raw material melting unit and the evaporation unit. The lower outlet of the melting kettle is connected to the inlet of the buffer tank, and the lower outlet of the buffer tank is connected to the inlet of the evaporator.

4. The apparatus according to claim 3, characterized in that, The buffer tank is also provided with a jacket on the outside, and heat transfer oil is circulated into the jacket for heat tracing.

5. The apparatus according to claim 3, characterized in that, A first delivery pump, which is a metering pump, is also provided between the melting kettle and the buffer tank.

6. The apparatus according to claim 1, characterized in that, The evaporator is a vacuum evaporator, including any one of a rising film evaporator, a falling film evaporator, or a scraped film evaporator.

7. The apparatus according to claim 1, characterized in that, The evaporator is equipped with a stirring assembly inside and a jacket on the outside.

8. The apparatus according to claim 1, characterized in that, The heating medium for the evaporator and evaporator kettle includes heat transfer oil.

9. The apparatus according to claim 1, characterized in that, The bottom outlet of the evaporator is also connected to a slag discharge tank.

10. The apparatus according to claim 9, characterized in that, A second conveying pump is also provided between the evaporation kettle and the slag discharge tank.

11. The apparatus according to claim 9, characterized in that, The bottom outlet of the slag discharge tank is connected in sequence to a solid waste slicer and a solid waste conveyor.

12. The apparatus according to claim 1, characterized in that, The distillation column includes a packed distillation column or a plate distillation column.

13. The apparatus according to claim 12, characterized in that, The distillation column is a packed distillation column.

14. The apparatus according to claim 1, characterized in that, Both the top condenser and the bottom reboiler of the tower use heat transfer oil as the heat exchange medium.

15. The apparatus according to claim 1, characterized in that, A third transfer pump is also provided between the distillation column and the product receiving tank.

16. The apparatus according to claim 1, characterized in that, The bottom outlet of the product receiving tank is sequentially connected to a product slicer, a product conveyor, and a product packaging machine.

17. The apparatus according to claim 1, characterized in that, The heat exchange medium of the exhaust gas condenser includes heat transfer oil.

18. The apparatus according to claim 1, characterized in that, The bottom outlet of the exhaust gas collector is connected to a buffer chamber.

19. The apparatus according to claim 1, characterized in that, The heat exchange medium of the exhaust gas trap includes circulating water or chilled water.

20. A method for extracting m-cyanobenzamide using the apparatus according to any one of claims 1-19, characterized in that, The method includes the following steps: (1) The non-conforming isophthalonitrile is melted and then subjected to two-stage evaporation. The liquid remaining after the first-stage evaporation is subjected to a second-stage evaporation. Both the first-stage and second-stage evaporation generate gas. The remaining material after the second-stage evaporation is discharged. The isophthalonitrile content of the non-conforming isophthalonitrile is 50~90wt%, and the content of isocyanobenzoamide is 0.01~40wt%. The two-stage evaporation is carried out in an evaporator and an evaporation kettle, respectively. The first-stage evaporation includes heating and vaporizing part of the isophthalonitrile and part of the isocyanobenzoamide in the non-conforming isophthalonitrile in the evaporator. The second-stage evaporation includes continuing to evaporate and vaporize the remaining high-boiling matter and the unvaporized non-conforming isophthalonitrile in the evaporation kettle. Finally, the remaining high-boiling matter is discharged from the bottom of the evaporation kettle. (2) The gas obtained by evaporation in step (1) is fed into a distillation column for distillation purification. The bottom of the distillation column is taken out as m-cyanobenzamide product, and the top of the distillation column is taken out as m-phthalonitrile.

21. The method according to claim 20, characterized in that, In step (1), the non-conforming isophthalonitrile product is first added to the melting kettle for melting, and then transported to the buffer tank.

22. The method according to claim 21, characterized in that, The melting temperature of the non-conforming isophthalonitrile is 160~260℃.

23. The method according to claim 22, characterized in that, The melting temperature of the non-conforming isophthalonitrile is 180~240℃.

24. The method according to claim 21, characterized in that, The heating medium used in the melting kettle and buffer tank includes heat transfer oil.

25. The method according to claim 24, characterized in that, The temperature of the heat transfer oil is 180~300℃.

26. The method according to claim 20, characterized in that, The non-conforming isophthalonitrile is melted and discharged by pumping, and is quantitatively delivered by metering pump.

27. The method according to claim 20, characterized in that, The temperature of the gas phase after heating and vaporization in the evaporator is 160~250℃.

28. The method according to claim 20, characterized in that, The temperature of the liquid phase inside the evaporator is 200~300℃.

29. The method according to claim 28, characterized in that, The temperature of the liquid phase inside the evaporator is 240~280℃.

30. The method according to claim 20, characterized in that, The vacuum levels in the evaporator and evaporator kettle are independently 55~99 kPa.

31. The method according to claim 30, characterized in that, The vacuum levels in the evaporator and evaporator kettle are independently 85~95 kPa.

32. The method according to claim 20, characterized in that, The evaporator and evaporation kettle are heated by heat transfer oil.

33. The method according to claim 32, characterized in that, The temperature of the heat transfer oil is 220~340℃.

34. The method according to claim 33, characterized in that, The temperature of the heat transfer oil is 240~320℃.

35. The method according to claim 20, characterized in that, The high-boiling-point substances include terephthalonitrile, m-cyanobenzoamide, and benzonitrile.

36. The method according to claim 35, characterized in that, The high-boiling-point substance is pumped into a slag discharge tank via a second transfer pump, and then cooled, sliced, and packaged.

37. The method according to claim 20, characterized in that, The feed to the distillation column in step (2) is a bubble point feed.

38. The method according to claim 20, characterized in that, The top temperature of the distillation column is 160~250℃.

39. The method according to claim 38, characterized in that, The top temperature of the distillation column is 160~200℃.

40. The method according to claim 20, characterized in that, The bottom temperature of the distillation column is 200~300℃.

41. The method according to claim 40, characterized in that, The bottom temperature of the distillation column is 250~280℃.

42. The method according to claim 20, characterized in that, The vacuum level of the distillation column is 55~99 kPa.

43. The method according to claim 42, characterized in that, The vacuum level of the distillation column is 85~98 kPa.

44. The method according to claim 20, characterized in that, The bottom liquid level of the distillation column is 0~3000mm.

45. The method according to claim 20, characterized in that, The distillation column uses heat transfer oil for heat exchange in both the top condenser and the bottom reboiler.

46. ​​The method according to claim 45, characterized in that, The feed temperature of the heat transfer oil in the top condenser of the tower is 150~240℃.

47. The method according to claim 46, characterized in that, The feed temperature of the heat transfer oil in the top condenser of the tower is 160~220℃.

48. The method according to claim 45, characterized in that, The feed temperature of the heat transfer oil in the reboiler at the bottom of the tower is 220~340℃.

49. The method according to claim 48, characterized in that, The feed temperature of the heat transfer oil in the reboiler at the bottom of the tower is 220~300℃.

50. The method according to claim 20, characterized in that, The bottom liquid product of the distillation column is sent to the product receiving tank by a third transfer pump, and then cooled, sliced ​​and packaged by a product slicer.

51. The method according to claim 20, characterized in that, The purity of the m-cyanobenzamide product is 80~99wt%.

52. The method according to claim 51, characterized in that, The purity of the m-cyanobenzamide product is 90~98wt%.

53. The method according to claim 20, characterized in that, The material at the top of the distillation column is condensed, and part of the condensate is collected and sent to the isophthalonitrile receiving tank to obtain the byproduct isophthalonitrile. Part of the condensate is refluxed for further distillation.

54. The method according to claim 53, characterized in that, The reflux ratio of the distillation column is 0.5 to 5.

55. The method according to claim 20, characterized in that, The uncondensed gas at the top of the distillation column passes through the tail gas condenser, and the condensate flows back to the isophthalonitrile receiving tank. The non-condensable components are then recovered by the tail gas trap.

56. The method according to claim 55, characterized in that, The exhaust gas condenser is cooled by heat transfer oil, and the inlet temperature of the heat transfer oil is 140~230℃.

57. The method according to claim 55, characterized in that, The exhaust gas collector is cooled by circulating water or chilled water, and the inlet temperature of the circulating water or chilled water is 1~50℃.

58. The method according to claim 57, characterized in that, The exhaust gas collector is cooled by circulating water or chilled water, and the inlet temperature of the circulating water or chilled water is 7~30℃.

59. The method according to claim 55, characterized in that, The byproduct captured by the exhaust gas trap is isophthalonitrile solid, which is packaged after passing through a buffer chamber.

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