Process and system for recovering plasticizer in plasticizing processing flue gas

Abstract

The invention relates to a process and a system for recovering a plasticizer in plasticizing processing flue gas, which realize efficient recovery of the plasticizer through combination of multi-stage condensation, negative pressure dehydration and rectification purification technologies, solve the problems of low purification efficiency and incapability of direct reuse after long-term use in the prior art, and realize efficient recovery and cyclic utilization of the plasticizer. And a heat pump waste heat recovery technology is integrated, so that environmental protection and economical efficiency are realized synchronously.

Description

Technical Field

[0001] This invention belongs to the field of cellulose acetate plastic processing technology, and relates to a process and system for recovering plasticizers from plasticizing process flue gas. Background Technology

[0002] Plasticizers are commonly used to improve the plasticizing and processing properties of materials. For example, a certain amount of plasticizer is usually added during the plasticizing and processing of cellulose diacetate. During melt extrusion processing, the material is heated to a high temperature, and the plasticizer and moisture in it volatilize, generating high-temperature flue gas.

[0003] Plasticizers are valuable chemical raw materials. Recycling them is not only necessary for pollution control and environmental protection, but also an effective way to save raw materials and reduce costs. For fixed plasticizing processes, the types of plasticizers used are relatively fixed, which provides excellent conditions for separation, purification, and reuse.

[0004] In high-temperature flue gas, plasticizers and moisture are suspended in the air as tiny liquid dispersions, forming aerosols. Currently, industrial methods for treating aerosols include mechanical centrifugal sedimentation, filtration and adsorption, high-temperature incineration, and high-voltage electrostatic treatment.

[0005] In existing technologies, plasticizer flue gas is a chemical oil gas that volatilizes when heated, and cannot be completely captured by mechanical methods. If filtration and adsorption methods are used, the filtration performance is greatly reduced after the filter media surface is coated with plasticizers. High-temperature incineration is a destruction method, which is not only costly to operate but also cannot recover plasticizers. High-voltage electrostatic methods utilize the Coulomb force in an electric field to directly act on tiny droplets, thus achieving high flue gas purification efficiency and being the most widely used method. However, this method also has two main drawbacks:

[0006] 1. Over time, the oil film thickens, reducing purification efficiency;

[0007] 2. When plasticizers are enriched together with water, an oil-water mixture is collected. If a higher purity plasticizer is desired, further oil-water separation is still required.

[0008] Furthermore, due to the differences in boiling points of different plasticizer components, the proportion of components volatilized under the same temperature conditions in the extruder differs significantly from the initial ratio. Even after separating the oil and water using simple techniques, the collected plasticizer cannot be directly reused, which will inevitably affect the plasticizer ratio of the mixture. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of reduced purification efficiency and inability to be directly reused after recycling in the prior art, and to provide a plasticizer recovery process in plasticizing process flue gas.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A process for recovering plasticizers from plasticizing processing flue gas includes the following steps:

[0012] (1) Condensation treatment: The flow rate of high-temperature flue gas is reduced by a gradually expanding flow channel, and the heat exchange is more complete so that the plasticizer and water vapor are condensed into liquid phase. The uncondensed gas phase is then condensed again.

[0013] (2) Oil-water separation: Separate the oil phase containing trace amounts of water from the condensate in step (1);

[0014] (3) Deep dehydration: The oil phase in step (2) is heated under a slight negative pressure environment to vaporize the residual water and achieve deep dehydration; the vaporized gas phase is condensed and circulated in the system to improve the recovery rate;

[0015] (4) Distillation purification: Under negative pressure conditions, the plasticizer after deep distillation is purified to separate different components.

[0016] Preferably, in step (3), the operating pressure of the falling film evaporator is 60-70 bar, the oil phase heating temperature is 80-95°C, and the vaporized gas phase is introduced into the cooler by an induced draft fan for condensation treatment.

[0017] Preferably, in step (3), the heat source of the falling film evaporator is provided by a heat pump device, which recovers process waste heat, including the waste heat of hot material taken from the bottom of the distillation column, or the waste heat of circulating water used to regulate the barrel temperature of the granulator unit.

[0018] Preferably, in step (4), the distillation column is a packed column and the operating pressure is 10-30 mbar.

[0019] Preferably, in step (4), the boiling point difference between the plasticizer components separated by the distillation column is greater than 30°C.

[0020] Preferably, the process is applicable to the recovery of triacetin and acetyl citrate or citrate mixed plasticizers, and the different components are adapted by adjusting the falling film evaporation temperature and distillation pressure.

[0021] Another object of the present invention is to provide a plasticizer recovery system in plasticizing process flue gas.

[0022] To achieve the second objective mentioned above, the technical solution adopted by the present invention is as follows:

[0023] A plasticizer recovery system from plasticizing processing flue gas includes:

[0024] Condenser: It is equipped with a gradually expanding flow channel that reduces the flow rate of high-temperature flue gas. The condenser inlet is connected to the high-temperature flue gas source, the condenser non-condensable gas outlet is connected to the cooler, and the bottom condensate outlet is connected to the stratifier.

[0025] Separator: The material inlet of the separator receives condensate, the bottom heavy phase outlet of the separator is connected to a falling film evaporator, and the light phase outlet of the upper separator discharges the aqueous phase.

[0026] Falling film evaporator: The falling film evaporator receives the oil phase at the material inlet, its top non-condensable gas outlet is connected to the cooler inlet, and its bottom dehydrated material outlet is connected to the distillation column;

[0027] Cooler: The cooler inlet receives gas from the non-condensable gas outlet of the condenser and the vaporized gas phase outlet of the falling film evaporator, condenses trace amounts of plasticizer and water therein, and the condensate is discharged to the stratifier through the outlet;

[0028] Distillation column: The distillation column receives dehydrated oil phase at the material inlet, low-boiling-point plasticizer at the top material outlet, and high-boiling-point plasticizer at the bottom material outlet;

[0029] Exhaust fan: The inlet of the exhaust fan is connected to the gas phase outlet of the cooler, and is used to introduce the high-temperature flue gas that is not completely condensed in the condenser and the gas phase volatilized in the falling film evaporator into the cooler for condensation again, and the purified flue gas is discharged from the outlet of the exhaust fan.

[0030] Heat pump unit: One side is connected to the reboiler of the distillation column or the circulating water of the granulation unit to absorb the waste heat, and the other side is connected to the falling film evaporator to provide heat to it; wherein, the falling film evaporator, the heat pump unit and the connecting pipes are filled with a heat transfer medium, and the heat pump unit transfers the heat absorbed from the waste heat to the heat transfer medium, and the heat transfer medium circulates in a closed loop in the pipes.

[0031] Preferably, the condenser has a gradually expanding flow channel cross-section to reduce airflow velocity and extend heat exchange time, thereby improving condensation efficiency; wherein the gradually expanding angle is 14-16°, and the ratio of the gradually expanding flow channel length to the inlet diameter is in the range of 4-6.

[0032] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include:

[0033] This invention, through an innovative combination of multi-stage condensation, negative pressure evaporation dehydration, and distillation purification technologies, not only solves the problems of reduced purification efficiency and inability to be directly reused after recovery in existing technologies, achieving efficient recovery and recycling of plasticizers, but also incorporates heat pump waste heat recovery technology, simultaneously achieving both environmental friendliness and economic efficiency. Using the recovery process of this invention, the total plasticizer recovery rate is ≥99%, the purified flue gas can directly meet emission standards, and the recovered plasticizer can be directly reused in the original production process without secondary blending. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the plasticizer recovery process in the plasticizing process flue gas of the present invention.

[0035] Figure 2 This is a schematic diagram of the heat transfer path of the heat pump device of the present invention.

[0036] Figure 3 This is a schematic diagram of a gradually expanding flow channel in a condenser.

[0037] The attached figures are labeled as follows:

[0038] 1-Condenser; 2-Separator; 3-Falling film evaporator; 4-Distillation column; 5-Heat pump unit; 6-Cooler; 7-Exhaust fan.

[0039] 11-Condenser inlet; 12-Condensate non-condensable gas outlet; 13-Condensate outlet;

[0040] 21 - Separator material inlet; 22 - Separator heavy phase outlet; 23 - Separator light phase outlet;

[0041] 31-Falling film evaporator material inlet; 32-Vaporized gas phase outlet; 33-Dehydrated material outlet;

[0042] 41 - Distillation column material inlet; 42 - Top material outlet; 43 - Bottom material outlet;

[0043] 51-Heat pump hot-side material inlet; 52-Heat pump hot-side material inlet; 53-Heat transfer medium outlet; 54-Heat transfer medium inlet;

[0044] 61-Cooler inlet; 62-Cooler non-condensable gas outlet; 63-Cooler condensate outlet;

[0045] 71 - Induced draft fan inlet; 72 - Induced draft fan outlet. Detailed Implementation

[0046] See Figure 1 , Figure 2As shown, this invention provides a plasticizer recovery system from plasticizing processing flue gas, comprising: a condenser, a separator, a falling film evaporator, a distillation column, and a heat pump unit; wherein, the condenser 1 is provided with a gradually expanding flow channel, the condenser inlet 11 is connected to a high-temperature flue gas source, the condenser non-condensable gas outlet 12 is connected to a cooler 6, and the bottom condensate outlet 13 is connected to the separator 2; the separator material inlet 21 receives condensate from the condenser 1 and the cooler 6, its bottom separator heavy phase outlet 22 is connected to the falling film evaporator, and its top separator light phase outlet 23 discharges the aqueous phase; the falling film evaporator material inlet 31 receives the oil phase, and its top non-condensable gas outlet 32 ​​is connected to... The cooler 6 is connected to the bottom dehydrated material outlet 33, which is connected to the distillation column 4. The distillation column material inlet 41 receives the dehydrated oil phase, the top material outlet 42 produces low-boiling-point plasticizer, and the bottom material outlet 43 (in chemical separation processes such as distillation and refrigeration, "bottom material" specifically refers to the liquid material accumulated in the bottom of the distillation column) produces high-boiling-point plasticizer. One side of the heat pump unit has heat pump hot-side material inlet 51 and heat pump hot-side material inlet 52, which are respectively connected to the bottom of the distillation column or the circulating water of the granulator unit. The other side has heat transfer medium outlet 53 and heat transfer medium inlet 54, which are respectively connected to the inlet and outlet of the heating pipeline of the falling film evaporator. The cooler 6 has a gas phase inlet 61 that receives non-condensable gas from the condenser 1 and the falling film evaporator 3, a gas phase outlet 62 that is connected to the induced draft fan 7, and a bottom condensate liquid phase outlet 63 that is connected to the separator 2. The induced draft fan 7 has an inlet 71 that is connected to the cooler and an outlet 72 that is discharged into the air.

[0047] In this embodiment, the flow channel cross-section of the condenser 1 adopts a gradually expanding design to reduce the airflow velocity and extend the heat exchange time, thereby improving the condensation efficiency.

[0048] In this embodiment, the inner wall of the evaporation chamber of the falling film evaporator 3 is made of 316L stainless steel.

[0049] In this embodiment, the induced draft fan 7 guides the non-condensable gas in the condenser 1 and the falling film evaporator 3 into the cooler 6 to fully condense the moisture and trace amounts of plasticizer therein. This arrangement can reduce plasticizer loss.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a process for recovering plasticizers from plasticizing processing flue gas, including: condensation of mixed oil and gas, primary oil-water separation, deep dehydration of the oil phase, and separation and purification. The condensation of the mixed oil and gas is completed by a condenser; primary oil-water separation is achieved by a separator; deep dehydration of the oil phase is completed in a falling film evaporator, where residual water in the collected oil phase is removed under negative pressure to obtain a crude plasticizer product with low water content; plasticizer separation and purification are completed by a distillation column to further separate different components and improve the purity of the recovered plasticizer; the specific process flow is as follows:

[0052] (1) Condensation Treatment: The high-temperature mixed flue gas enters condenser 1 through condenser inlet 11. The condenser has a gradually expanding angle of 15°, and the ratio of the length of the gradually expanding channel to the inlet diameter is 5. Due to the increased cross-section of the channel, the airflow velocity is reduced from 25 m / s to 8 m / s, and the residence time is extended, which is conducive to sufficient heat exchange. Compared with the straight tube type, the condensation efficiency is increased by 30%. After heat exchange, part of the flue gas condenses into a liquid phase, which flows naturally to the bottom of the condenser under gravity. The condensate is discharged from the bottom condensate outlet 13 and then collected in the separator 2 through the separator material inlet. Among them, the non-condensable gas in the high-temperature mixed flue gas is discharged through the condenser non-condensable gas outlet 12 and enters the cooler 6, and is connected to the induced draft fan after the cooler non-condensable gas outlet. The induced draft fan is used to introduce the high-temperature flue gas that is not completely condensed in condenser 1 and the gas phase volatilized in falling film evaporator 3 into cooler 6 for condensation again.

[0053] (2) Oil-water separation: In the separator 2, the plasticizer and water are not miscible and naturally separate into layers. However, since the lower oil phase still contains trace amounts of water, the bottom heavy phase outlet of the separator 2 is connected to the falling film evaporator and pumped to the material inlet 31 of the falling film evaporator at the top of the falling film evaporator 3; the water phase is discharged from the top light phase outlet of the separator.

[0054] (3) Deep Dehydration: The falling film evaporator is equipped with a vacuum device to provide negative pressure, so that the evaporation chamber of the falling film evaporator 3 is under negative pressure. Because the boiling point of water is much lower than that of plasticizer, under negative pressure, the trace amount of water contained in the oil phase will vaporize again in the evaporation chamber after being heated in the falling film evaporator 3. Under the action of the induced draft fan, it will be discharged from the non-condensable gas outlet 32 ​​and flow into the cooler 6. The plasticizer carried by the trace amount of water vapor will also be re-condensed. During this period, the plasticizer with a higher boiling point remains in the liquid phase and naturally sinks to the bottom of the falling film evaporator 3 under the action of gravity. It will merge with the liquid phase at the bottom of the evaporation chamber and be discharged from the dehydrated material outlet 33. At this time, almost all the water in the plasticizer has been removed.

[0055] It should be noted that in this embodiment, the operating pressure of the falling film evaporator is 60-70 bar, the oil phase heating temperature is 80-95°C, and the vaporized gas phase is guided by an induced draft fan to a cooler for condensation. The heat source for the falling film evaporator is provided by a heat pump unit, which recovers process waste heat, including the waste heat from the hot material collected from the bottom of the distillation column or the waste heat from the circulating water used to regulate the barrel temperature of the granulator unit. One side of the heat pump unit is connected to the distillation column bottom or the circulating water of the granulator unit, and the other side provides heat to the falling film evaporator (specifically as follows). Figure 2 (As shown).

[0056] (4) Distillation purification: The plasticizer after the water has been removed enters the distillation column 4 through the material inlet 41 of the distillation column. The components are separated by the difference in boiling point. The plasticizer component with a relatively low boiling point is obtained at the material outlet 42 at the top of the distillation column, and the plasticizer component with a relatively high boiling point is obtained at the material outlet 43 at the bottom of the distillation column.

[0057] It should be noted that in this embodiment, the distillation column 4 is a packed column with an operating pressure of 10-30 mbar. Different components are separated by the difference in boiling points, and the purity of the plasticizers collected from the top and bottom of the column is higher than 99%. The boiling point difference between the plasticizer components separated by the distillation column is greater than 30°C, and the recovered plasticizer can be directly reused in the original production process without secondary blending.

[0058] In summary, the induced draft fan of this invention introduces the uncondensed gas phase from the condenser and the dehydrated vaporized gas phase from the falling film evaporator into the cooler, achieving full recovery of plasticizers entrained in the gas phase, with the total recovery rate increased to ≥99%. Secondly, the heat pump device 5 is used to recover waste heat and provide thermal energy to the falling film evaporator, reducing external energy consumption by 30%-50%. In addition, the operating pressure of the distillation column (10-30 mbar) is adjusted according to the boiling point differences (ΔT≥30℃) of different plasticizer combinations to ensure the accuracy of component separation.

[0059] Example 2

[0060] A process for recovering plasticizers from plasticizing flue gas, for a mixed plasticizer of triacetin and triethyl acetyl citrate, includes the following steps:

[0061] (1) The high-temperature mixed flue gas is drawn into the condenser through the condenser inlet 11. The condenser has a gradually expanding angle of 14° and the ratio of the length of the gradually expanding channel to the inlet diameter is 6. In the condenser, the plasticizer and moisture are condensed into liquid phase and flow into the separator. The gas phase is drawn out from the non-condensable gas outlet 12 by the induced draft fan and flows into the cooler inlet 61. It is condensed into liquid phase again and flows into the separator.

[0062] (2) In the separator, the density of the plasticizer is greater than that of water. The plasticizer and water naturally separate into heavy oil phases.

[0063] (3) The oil phase is then pumped to the falling film evaporator and heated to about 90°C. The trace amount of water contained therein evaporates and vaporizes. The gas phase is drawn out from the non-condensable gas outlet 32 ​​by the induced draft fan and flows into the cooler inlet 61 to be condensed again. The trace amount of plasticizer carried in the gas phase will also be condensed back into liquid phase and flow into the separator.

[0064] (4) After dehydration, the oil phase is pumped to the distillation column. Under a pressure of 20 mbar, 99.6% of triacetin is collected from the top of the column and 99.8% of acetylic acid triethyl ester is collected from the bottom of the column.

[0065] Example 3

[0066] A process for recovering plasticizers from plasticizing processing flue gas, for a mixed plasticizer of triacetin and triethyl citrate, includes the following steps:

[0067] (1) The high-temperature mixed flue gas is drawn into the condenser through the condenser inlet 11. The condenser has a gradually expanding angle of 16° and the ratio of the length of the gradually expanding channel to the inlet diameter is 4. In the condenser, the plasticizer and moisture are condensed into liquid phase and flow into the separator. The gas phase is drawn out from the non-condensable gas outlet 12 by the induced draft fan and flows into the cooler inlet 61. It is condensed into liquid phase again and flows into the separator.

[0068] (2) In the separator, the density of the plasticizer is greater than that of water. The plasticizer and water naturally separate into heavy oil phases.

[0069] (3) The oil phase is then pumped to the falling film evaporator and heated to about 85°C. The trace amount of water contained therein evaporates and vaporizes under the heat. The gas phase is drawn out from the 32 interface under the action of the induced draft fan and flows into the cooler inlet 61 to be condensed again. The trace amount of plasticizer carried in the gas phase will also be condensed back into liquid phase and flow into the separator.

[0070] (4) After dehydration, the oil phase is pumped to the distillation column. Under a pressure of 26 mbar, 99.1% triacetin is collected from the top of the column and 99.6% triethyl citrate is collected from the bottom of the column.

[0071] Example 4

[0072] A process for recovering plasticizers from plasticizing processing flue gas, for a mixed plasticizer of triacetin and tributyl citrate, includes the following steps:

[0073] (1) The high-temperature mixed flue gas is drawn into the condenser through the condenser inlet 11. The condenser has a gradually expanding angle of 15° and the ratio of the length of the gradually expanding channel to the inlet diameter is 5.5. In the condenser, the plasticizer and moisture are condensed into liquid phase and flow into the separator. The gas phase is drawn out from the non-condensable gas outlet 12 by the induced draft fan and flows into the cooler inlet 61. It is condensed into liquid phase again and flows into the separator.

[0074] (2) In the separator, the density of the plasticizer is greater than that of water. The plasticizer and water naturally separate into heavy oil phases.

[0075] (3) The oil phase is then pumped to the falling film evaporator and heated to about 89°C. The trace amount of water contained therein evaporates and vaporizes. The gas phase is drawn out from the 32 interface under the action of the induced draft fan and flows into the cooler inlet 61 to be condensed again. The trace amount of plasticizer carried in the gas phase will also be condensed back into liquid phase and flow into the separator.

[0076] (4) After dehydration, the oil phase is pumped back to the paper distillation column. Under a pressure of 18 mbar, 99.0% of triacetin is collected from the top of the column and 99.3% of tributyl citrate is collected from the bottom of the column.

[0077] Example 5

[0078] A process for recovering plasticizers from plasticizing processing flue gas, for a mixed plasticizer of triacetin and acetylthiose tributyl citrate, includes the following steps:

[0079] (1) The high-temperature mixed flue gas is drawn into the condenser through the condenser inlet 11. The condenser has a gradually expanding angle of 15° and the ratio of the length of the gradually expanding channel to the inlet diameter is 4.5. In the condenser, the plasticizer and moisture are condensed into liquid phase and flow into the separator. The gas phase is drawn out from the non-condensable gas outlet 12 by the induced draft fan and flows into the cooler inlet 61. It is condensed into liquid phase again and flows into the separator.

[0080] (2) In the separator, the density of the plasticizer is greater than that of water. The plasticizer and water naturally separate into heavy oil phases.

[0081] (3) The oil phase is then pumped to the falling film evaporator and heated to about 81°C. The trace amount of water contained therein evaporates and vaporizes. The gas phase is drawn out from the 32 interface under the action of the induced draft fan and flows into the cooler inlet 61 to be condensed again. The trace amount of plasticizer carried in the gas phase will also be condensed back into liquid phase and flow into the separator.

[0082] (4) After dehydration, the oil phase is pumped back to the paper distillation column. Under a pressure of 13 mbar, 99.1% of triacetin is collected from the top of the column and 99.5% of acetylic acid tributyl is collected from the bottom of the column.

[0083] The foregoing descriptions and embodiments are provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these contents, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the foregoing descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from its scope should be within the protection scope of the present invention.

Claims

1. A process for recovering plasticizers from plasticizing processing flue gas, characterized in that, Includes the following steps: (1) Condensation treatment: The flow rate of high-temperature flue gas is reduced by a gradually expanding flow channel, and the heat exchange is more complete so that the plasticizer and water vapor are condensed into liquid phase. The uncondensed gas phase is then condensed again. (2) Oil-water separation: Separate the oil phase containing trace amounts of water from the condensate in step (1); (3) Deep dehydration: The oil phase in step (2) is heated under a slight negative pressure environment to vaporize the residual water and achieve deep dehydration; the vaporized gas phase is condensed and circulated in the system to improve the recovery rate; (4) Distillation purification: Under negative pressure conditions, the plasticizer after deep distillation is purified to separate different components.

2. A plasticizer recovery system for plasticizing processing flue gas based on the process described in claim 1, characterized in that, include: Condenser: It is equipped with a gradually expanding flow channel that reduces the flow rate of high-temperature flue gas. The condenser inlet is connected to the high-temperature flue gas source, the condenser non-condensable gas outlet is connected to the cooler, and the bottom condensate outlet is connected to the stratifier. Separator: The material inlet of the separator receives condensate, the bottom heavy phase outlet of the separator is connected to a falling film evaporator, and the light phase outlet of the upper separator discharges the aqueous phase. Falling film evaporator: The falling film evaporator receives the oil phase at the material inlet, its top non-condensable gas outlet is connected to the cooler inlet, and its bottom dehydrated material outlet is connected to the distillation column; Cooler: The cooler inlet receives gas from the non-condensable gas outlet of the condenser and the vaporized gas phase outlet of the falling film evaporator, condenses trace amounts of plasticizer and water therein, and the condensate is discharged to the stratifier through the outlet; Distillation column: The distillation column receives dehydrated oil phase at the material inlet, low-boiling-point plasticizer at the top material outlet, and high-boiling-point plasticizer at the bottom material outlet; Exhaust fan: The exhaust fan inlet is connected to the cooler gas phase outlet, which is used to introduce the high temperature flue gas that is not completely condensed in the condenser and the gas phase volatilized in the falling film evaporator into the cooler for condensation again, and the exhaust fan outlet discharges the purified flue gas. Heat pump unit: One side is connected to the reboiler of the distillation column or the circulating water of the granulation unit to absorb the waste heat, and the other side is connected to the falling film evaporator to provide heat to it; wherein, the falling film evaporator, the heat pump unit and the connecting pipes are filled with a heat transfer medium, and the heat pump unit transfers the heat absorbed from the waste heat to the heat transfer medium, and the heat transfer medium circulates in a closed loop in the pipes.

3. The system according to claim 2, characterized in that: The condenser adopts a gradually expanding flow channel cross-section design to reduce airflow velocity and extend heat exchange time, thereby improving condensation efficiency; wherein, the gradually expanding angle is 14-16°, and the ratio of the gradually expanding flow channel length to the inlet diameter is in the range of 4-6.

4. The process according to claim 1, characterized in that: In step (3), the operating pressure of the falling film evaporator is 60-70 bar, the oil phase heating temperature is 80-95°C, and the vaporized gas phase is introduced into the cooler by an induced draft fan for condensation treatment.

5. The process according to claim 1, characterized in that: In step (3), the heat source of the falling film evaporator is provided by a heat pump device, which recovers process waste heat, including the waste heat material taken from the bottom of the distillation column, or the waste heat of the circulating water used to regulate the barrel temperature of the granulator unit.

6. The process according to claim 1, characterized in that: In step (4), the distillation column is a packed column with an operating pressure of 10-30 mbar.

7. The process according to claim 1, characterized in that: The process is applicable to the recovery of triacetin and acetyl citrate or citrate mixed plasticizers, and can be adapted to different components by adjusting the falling film evaporation temperature and distillation pressure.

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