CN113019259A - Vacuum adjusting method for polycondensation reaction device and vacuum system used by same - Google Patents
Vacuum adjusting method for polycondensation reaction device and vacuum system used by same Download PDFInfo
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- CN113019259A CN113019259A CN201911356325.2A CN201911356325A CN113019259A CN 113019259 A CN113019259 A CN 113019259A CN 201911356325 A CN201911356325 A CN 201911356325A CN 113019259 A CN113019259 A CN 113019259A
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Abstract
The invention discloses a vacuum system for a polycondensation reaction device and an adjusting method thereof, wherein the vacuum system comprises a vacuum absorption tank and a vacuum pump, the vacuum absorption tank is provided with a liquid phase inlet, a liquid phase outlet, a gas phase inlet communicated with the polycondensation reaction device and a gas phase outlet communicated with the vacuum pump, the liquid phase outlet is higher than the liquid phase inlet, the gas phase inlet and the gas phase outlet are both higher than the liquid phase outlet, the gas phase inlet extends inwards along the vacuum absorption tank to form an air inlet pipe, and the outlet end face of the air inlet pipe is flush with the bottom end of the liquid phase outlet. The liquid phase absorption mode is adopted, so that micromolecule compounds contained in gas-phase substances generated by the polycondensation reaction can be completely absorbed, the blockage or corrosion to a vacuum pump pipeline is avoided, the stability and long-period operation of a vacuum system in the production process are ensured, and meanwhile, the fine adjustment of the pressure in the vacuum absorption tank is realized through the liquid level adjustment in the vacuum absorption tank, so that the vacuum degree of the polycondensation reaction device is accurately controlled, and the operation is convenient.
Description
Technical Field
The invention relates to a vacuum adjusting method for a polycondensation reaction device and a vacuum system used by the same, in particular to a vacuum adjusting method for a polycondensation reaction device with micromolecule byproducts and a vacuum system used by the same, belonging to the technical field of polycondensation reaction.
Background
In the chemical industry, polycondensation plays an important role in polymer synthesis, and the application is very wide. Polymers such as polyesters, polyamides, phenolic resins, epoxy resins, polycarbonates, polyimides, and polyphenylene sulfides are prepared by polycondensation.
The polycondensation reaction is carried out by reacting active functional groups with each other and repeating the condensation for several times to form a polycondensation product. During the polycondensation reaction, small molecular by-products are usually removed, and the small molecular by-products are removed from the reaction system in time to promote the reversible reaction to be carried out in the forward direction, so that a high molecular weight product is finally obtained.
Taking the melt transesterification polycondensation process for the preparation of Polycarbonate (PC) as an example, the preparation process is generally divided into two reaction stages: in the ester exchange stage, bisphenol A (BPA) and diphenyl carbonate (DPC) in a molten state undergo ester exchange reaction to remove phenol (PhOH) to form oligomers, and about 95% of phenol by-product is theoretically removed in the stage; and in the polycondensation reaction stage, residual phenol and unreacted excessive DPC are further removed under the conditions of higher temperature and higher vacuum to generate PC with high molecular weight. In order to obtain a high molecular weight product, the pressure is reduced in stages throughout the process to remove reaction by-products, and the transesterification and polycondensation reactions are promoted to proceed in a forward direction. Under the same reaction temperature condition, PC resin products with different brands can be obtained under different vacuum degrees. Therefore, the vacuum system is a key component of the polycarbonate synthesis apparatus, and provides the necessary pressure conditions for the PC synthesis process, and the accuracy and stability of the control are crucial to the PC resin performance.
The PC polycondensation stage is kept at a high vacuum, and the quality of the PC resin is affected by small fluctuation of the vacuum degree in the polycondensation reaction device. The vacuum pumping process can entrain by-product phenol, a small amount of oligomers and unreacted excessive DPC, wherein the unreacted DPC, the oligomers and most of phenol and other distillates are condensed and recovered, but a small amount of residual distillates can be brought into a vacuum system. The freezing point of distillate phenol is high, and the distillate phenol can be solidified in a vacuum pipeline and a vacuum pump after leaving a high-temperature reaction kettle, so that the pipeline is blocked, the vacuum control is unstable, and the requirement of long-time stable high vacuum required by continuous production cannot be met. If phenol enters the vacuum pump, the phenol can corrode the pump body, pollute the operating medium (such as water and the like) of the pump and is not in line with the requirement of environmental protection.
And a direct esterification method (PTA method) to prepare thermoplastic polyesters such as polyethylene terephthalate (PET)/polytrimethylene terephthalate (PTT)/polybutylene terephthalate (PBT). The preparation process comprises two stages of esterification and polycondensation, wherein the first stage is to generate dihydroxyethyl terephthalate (BHET)/dihydroxypropyl terephthalate (BHPT)/dihydroxybutyl terephthalate (BHBT) by the esterification reaction of high-Purity Terephthalic Acid (PTA) and Ethylene Glycol (EG)/1, 3-Propanediol (PDO)/1, 4-Butanediol (BDO), and then the second stage is to perform polycondensation reaction on the BHET/BHPT/BHBT at high temperature and high vacuum to remove EG/PDO/BDO and generate the product PET/PTT/PBT. Along with the increase of the molecular weight of the reaction by-product, the requirement on the vacuum degree control of the reaction device is higher, and meanwhile, small molecular compounds entrained in the gas phase are easier to condense in a vacuum pipeline or a vacuum pump, so that the stability and the control precision of a vacuum system are damaged.
Therefore, it is highly desirable to develop a vacuum regulating system capable of ensuring a stable vacuum environment required in the production process of the polycondensation reaction, realizing a long-cycle operation, and simultaneously, accurately and smoothly regulating and controlling the vacuum degree of the polycondensation reaction apparatus.
The prior patent document CN104607105A (elution system and elution method for polyethylene terephthalate production equipment, 2015.05.13) provides a vacuum system composed of a glycol vacuum spraying system, a bent vacuum tail pipe and a vacuum unit, and the bent vacuum tail pipe can be sprayed and washed by the design of a spraying pipeline and a washing pipeline, so that the vacuum system of the polycondensation kettle can operate stably, and the hidden trouble and trouble of the vacuum system blockage can be solved.
The prior patent document CN206616173U (a continuous recycling PET apparatus, 2017.11.07) also provides a design that two sets of vacuum systems are respectively connected to the polycondensation reaction kettle, each set of vacuum system is composed of a sprayer, a vacuum adsorption buffer tank and a mechanical vacuum pump set, and the two sets of vacuum systems are arranged to be mutually standby, so as to solve the problem that the vacuum systems are easily blocked.
It can be known from the above patent documents that the vacuum system used in the existing polycondensation apparatus does not fundamentally solve the drawbacks of the polycondensation reaction process, and it substantially solves the technical solutions of how to clean the blocked vacuum pipeline and how to continue the continuous production after the vacuum pipeline is blocked.
Disclosure of Invention
The invention aims to provide a vacuum adjusting method for a polycondensation reaction device, which realizes fine adjustment of the pressure in a vacuum absorption tank by adjusting the liquid level in the vacuum absorption tank, thereby accurately controlling the vacuum degree of the polycondensation reaction device and being convenient to operate.
Another object of the present invention is to provide a vacuum system for a polycondensation reaction apparatus, which can completely absorb small molecular compounds contained in a gas phase substance generated by a polycondensation reaction by using a liquid phase absorption method, thereby preventing a vacuum pump pipeline from being blocked or corroded, and ensuring the stability and long-term operation of the vacuum system in a production process.
The invention is realized by the following technical scheme: a vacuum regulation method for polycondensation reactor features that a vacuum system is used, which includes vacuum sucking tanks communicated to polycondensation reactor and vacuum pump, and the liquid level in vacuum sucking tank is controlled to regulate the vacuum degree in polycondensation reactor.
Establish liquid phase import, liquid phase export, intercommunication polycondensation reaction unit's gaseous phase import and the gaseous phase export of intercommunication vacuum pump on the vacuum absorption jar, the liquid phase export is higher than the liquid phase import, gaseous phase import and gaseous phase export all are higher than the liquid phase export, and the gaseous phase import inwards extends along the vacuum absorption jar and forms the intake pipe, and the export terminal surface of intake pipe flushes with the bottom of liquid phase export.
The liquid level in the vacuum absorption tank is ensured to be higher than or equal to the outlet end surface of the air inlet pipe.
And arranging an absorption liquid tank to enable absorption liquid to circularly flow between the vacuum absorption tank and the absorption liquid tank along the liquid phase inlet and the liquid phase outlet, wherein the flow of the absorption liquid at the liquid phase outlet is adjusted according to the pressure at the gas phase outlet.
And controlling the pressure of the gas-phase inlet to be equal to the pressure in the polycondensation reaction device, and controlling the pressure of the vacuum absorption tank to be equal to the pressure of the absorption liquid tank.
The boiling point of the absorption liquid is more than or equal to 130 ℃, and the absorption liquid is mutually soluble with the micromolecule compound contained in the gas phase generated by the polycondensation reaction but does not generate chemical reaction.
The present invention also provides a vacuum system as described in the vacuum regulation method for a polycondensation reaction apparatus.
The vacuum absorption tank is provided with a pressure gauge, and a pipeline connected with the liquid phase outlet is provided with a flow regulating valve.
The liquid phase inlet and the liquid phase outlet are respectively communicated with an absorption liquid tank.
And a gas phase balance pipe is arranged between the vacuum absorption tank and the absorption liquid tank.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) the invention can ensure the stable operation of the polycondensation reaction process, and the gas phase can be ensured to be fully contacted with the absorption liquid because the outlet of the gas inlet pipe in the vacuum absorption tank is always immersed under the absorption liquid level, so that the carried micromolecular compound can be completely absorbed by the absorption liquid. The vacuum absorption tank and the pipeline between the tank body and the vacuum pump are prevented from being blocked by solidified micromolecular compounds, the vacuum pump body is also prevented from being blocked or corroded, and the stability and long-period operation of the vacuum system control in the production process are ensured.
(2) The invention adopts the absorption liquid tank to provide absorption liquid for the vacuum absorption tank, can detect the concentration of the micromolecule compound in the absorption liquid tank by periodically sampling the absorption liquid in the absorption liquid tank, empties the absorption liquid in the absorption liquid tank when the saturation concentration is approached, and then replenishes new absorption liquid to ensure the effect of the absorption liquid for absorbing the micromolecule compound.
(3) The invention adopts a liquid phase absorption mode, small molecular compounds carried in a gas phase generated by polycondensation are condensed and recovered and then absorbed by absorption liquid, and the small molecular compounds are completely absorbed by the absorption liquid in practical application, so that the pollution to running media (such as water and the like) of a pump is avoided, and the requirements of environmental protection can be met.
(4) The absorption liquid can be selected according to the characteristics of a polycondensation reaction system, and the polycondensation reaction is usually carried out under the conditions of high temperature and high negative pressure, so the absorption liquid has high boiling point and stable physicochemical property, and can be mutually dissolved with the small molecular compound carried in a gas phase without chemical reaction.
(5) The invention can realize the accurate control of the vacuum condition in the polycondensation reaction process, the outlet end surface of the air inlet pipe in the vacuum absorption tank is flush with the bottom end of the liquid phase outlet, the outlet of the air inlet pipe is ensured to be always immersed under the liquid level of the absorption liquid, the flow regulating valve of the liquid phase outlet can control the outlet flow through the automatic control system in the operation process, the opening degree and the liquid level height are in inverse proportion, thereby regulating the vacuum degree of the polycondensation reaction device, and the operation is simple and easy.
(6) The invention can realize the automatic control of the vacuum degree, adopts the automatic interlocking control of the valve, namely, a pressure gauge and a flow regulating valve are respectively designed at each control point position, the pressure gauge respectively reflects the gas phase inlet pressure and the gas phase outlet pressure, the flow regulating valve is used for realizing the control of the flow of the liquid phase outlet so as to control the liquid level height of the absorption liquid, and finally, the vacuum degree of the polycondensation reaction device is accurately regulated.
Drawings
Fig. 1 is a flowchart of a vacuum system according to embodiment 1 of the present invention.
Fig. 2 is a schematic structural view of a vacuum absorption tank according to embodiment 1 of the present invention.
Fig. 3 is a flowchart of a vacuum system according to embodiment 3 of the present invention.
Fig. 4 is a schematic structural view of a vacuum absorption tank according to embodiment 3 of the present invention.
Fig. 5 is a control diagram for regulating the vacuum system according to the present invention.
The system comprises a vacuum absorption tank 1, a liquid phase inlet 2, a liquid phase outlet 3, a gas phase inlet 4, a gas phase outlet 5, a polycondensation reaction device 6, an air inlet pipe 7, a pressure gauge 8, a liquid level meter 9, a flow regulating valve 10, an absorption liquid tank 11, a gas phase balance pipe 12, a condensation recovery tank 13, a gas phase balance pipe joint 14, a jacket cooling inlet 15, a jacket cooling outlet 16, a jacket cooling outlet 17, a liquid delivery pump 18 and a pressure gauge joint 19.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
Example 1:
the present embodiment relates to a vacuum system for a polycondensation reaction apparatus.
The vacuum system mainly comprises a vacuum absorption tank 1 and a vacuum pump, and is used for continuously vacuumizing the polycondensation reaction device 6 so as to ensure high vacuum pressure in the polycondensation reaction device 6. As shown in fig. 1, the polycondensation reaction apparatus 6 is generally provided with at least one condensation recovery tank 13, the condensation recovery tank 13 forms a gas phase passage communicating with the vacuum absorption tank 1 and the vacuum pump, the condensation recovery tank 13 is used for condensing and recovering unreacted excess monomers, a small amount of oligomers and by-products removed in the polycondensation reaction, and the condensed and recovered gas phase substance is sent to the vacuum absorption tank 1 again.
The vacuum absorption tank 1 adopts the structure shown in fig. 2, a liquid phase inlet 2, a liquid phase outlet 3, a gas phase inlet 4 and a gas phase outlet 5 are respectively arranged on the vacuum absorption tank 1, the gas phase inlet 4 is communicated with a condensation recovery tank 13, the gas phase outlet 5 is communicated with a vacuum pump, and the liquid phase inlet 2 and the liquid phase outlet 3 are respectively communicated with an absorption liquid tank 11. The liquid phase outlet 3, the absorption liquid tank 11 and the liquid phase inlet 2 form a liquid phase passage communicated with the vacuum absorption tank 1 and are used for filling the vacuum absorption tank 1 with sufficient absorption liquid. The micromolecule compound contained in the gas-phase substance can be completely absorbed in the vacuum absorption tank 1 in a liquid-phase absorption mode, so that the gas-phase inlet 4 and the gas-phase outlet 5 are higher than the liquid-phase outlet 3 on the structure of the vacuum absorption tank 1, and meanwhile, the gas-phase inlet 4 extends inwards along the vacuum absorption tank 1 to form the air inlet pipe 7, so that the outlet end face of the air inlet pipe 7 is flush with the bottom end of the liquid-phase outlet 3. When in use, when the absorption liquid circularly flows between the vacuum absorption tank 1 and the absorption liquid tank 11, the outlet of the air inlet pipe 7 can be ensured to be always immersed in the absorption liquid, and the liquid phase absorption of the micromolecular compound is realized. In order to ensure that the gas phase pressure of the two tank bodies is the same and the absorption liquid can be stably conveyed, a gas phase balance pipe 12 is also arranged between the vacuum absorption tank 1 and the absorption liquid tank 11.
In this embodiment, the absorption liquid should be selected according to the characteristics of the polycondensation reaction system. Since the polycondensation reaction is usually carried out under high temperature and high negative pressure conditions, the absorption liquid should have a high boiling point (boiling point ≥ 130 ℃, preferably 180 ℃), stable physicochemical properties, and be miscible with the small molecule compound carried in the gas phase but not undergo a chemical reaction. For example, in one possible embodiment, the absorbent is selected from polyols such as C2-C12 diols, triols, etc., or preferably ethylene glycol and 1, 3-propanediol.
The vacuum system can realize complete absorption of micromolecular compounds and can also adjust the vacuum pressure of the micromolecular compounds, as shown in the structure of figure 5, the vacuum system is realized by arranging a pressure gauge 8 and a liquid level meter 9 on a vacuum absorption tank 1 and arranging a flow regulating valve 10 on a pipeline connected with a liquid phase outlet 3, the pressure gauge 8 is used for measuring the pressure of a gas phase inlet 4 and the pressure of a gas phase outlet 5, and the liquid level meter 9 is used for measuring the liquid level height which is higher than the bottom end of the liquid phase outlet 3 in the vacuum absorption tank 1. When the device is used, the liquid level height in the vacuum absorption tank 1 can be controlled through the flow regulating valve 10, so that the vacuum degree in the polycondensation reaction device 6 is regulated, and the accurate control of the vacuum degree in the polycondensation reaction device 6 is realized.
Example 2:
this example relates to a conditioning method for the vacuum system described in example 1.
The method is mainly to adjust the vacuum degree in the polycondensation reaction device 6 by controlling the liquid level height in the vacuum absorption tank 1. In the practical application process, the following contents are specifically included:
guarantee that the liquid level height in the vacuum absorption jar 1 is higher than the certain height of the outlet end face of intake pipe 7 all the time or level with the liquid level for the absorption liquid circulates between vacuum absorption jar 1 and absorption fluid reservoir 11 along liquid phase import 2 and liquid phase export 3, during this period, the flow size (the aperture of flow control valve 10) of the absorption liquid of liquid phase export 3 is adjusted according to the pressure of gaseous phase export 5 department, and simultaneously, the pressure of control gaseous phase import 4 equals with the pressure in polycondensation reaction device 6, can realize the regulation of vacuum pressure in polycondensation reaction device 6, of course, for better realization vacuum pressure regulation in the vacuum absorption jar 1, the pressure that still should control vacuum absorption jar 1 equals with the pressure of absorption fluid reservoir 11, be convenient for the steady transport of absorption liquid.
The specific adjustment process can be summarized as follows:
the calculation formula of the pressure difference between the outlet of the air inlet pipe 7 and the liquid level of the absorption liquid is as follows:
wherein rho is the density of the absorption liquid, g is the gravity acceleration, and h is the height difference between the outlet of the air inlet pipe 7 (the bottom end of the liquid phase outlet 3) and the liquid level in the vacuum absorption tank 1.
Therefore, the pressure (absolute pressure) at the gas phase inlet 4 of the vacuum absorption tank 1 is:
and the pressure of the gas phase inlet 4 is equal to the pressure in the polycondensation reaction device 6 in the main process flow, so that the degree of vacuum in the polycondensation reaction device 6 can be finely adjusted to a certain degree by controlling the opening of the flow regulating valve 10 of the liquid phase outlet 3 of the vacuum absorption tank 1.
Meanwhile, the liquid level meter 9, the pressure of the gas phase inlet 4, the pressure of the gas phase outlet 5 and the regulating valve of the liquid phase outlet 3 can be embodied or regulated in an automatic control system, so that the accurate control of the vacuum degree in the polycondensation reaction device 6 is realized.
Example 3:
this example takes the preparation of PC by melt transesterification polycondensation as an example, and provides a vacuum system and a regulating method for use therewith.
As shown in fig. 3, the vacuum adjusting system according to the present embodiment includes: a vacuum absorption tank 1, an absorption liquid tank 11 and a vacuum pump.
The vacuum system in the polycondensation stage is sequentially connected with: a polycondensation reaction device 6, a condensation recovery tank (a), a condensation recovery tank (b), a vacuum absorption tank 1 and a vacuum pump.
In the process of producing PC by the melt transesterification polycondensation method, the by-product phenol, unreacted excess DPC and a small amount of oligomer removed from the polycondensation reaction system leave the polycondensation reaction device 6 along with the gas phase, and enter a condensation recovery tank (a) and a condensation recovery tank (b). DPC and oligomers and most of the phenol are condensed in two condensation recovery tanks 13 in series, but a small amount of phenol will still enter the subsequent vacuum absorption tank 1.
As shown in fig. 4 and 5, the vacuum absorption tank 1 includes:
gas phase passage: comprising a gas phase inlet 4, a gas phase outlet 5 and a gas phase equilibrium tube interface 14.
Liquid phase passage: comprising a liquid phase inlet 2 and a liquid phase outlet 3.
A vacuum adjusting part: comprises a pressure gauge 8, a liquid level meter 9 and a flow regulating valve 10.
Vacuum absorption tank 1: the tank body is filled with an absorbing liquid selected from polyhydric alcohols such as dihydric alcohol and trihydric alcohol of C2-C12, preferably ethylene glycol.
Cooling jacket: comprising a jacket cooling inlet 15, a jacket 16 and a jacket cooling outlet 17.
An automatic control system: a polycondensation reaction device 6 is provided with a pressure remote transmission site A (PT-1101), a liquid phase outlet 3 of a vacuum absorption tank 1 is provided with a flow regulating site B (FV-2101), a pressure gauge port 19 of the vacuum absorption tank 1 is provided with a pressure display site C (PI-2101), and a liquid level remote transmission site D (LT-2101) is arranged in the vacuum absorption tank 1. The four sites are integrated into an automatic control system and are accurately regulated and controlled by the automatic control system.
The working process of the vacuum regulation system in this embodiment is as follows:
the gas phase extracted from the condensation recovery tank 13 enters the vacuum absorption tank 1 from the gas phase inlet 4, and the outlet of the gas inlet pipe 7 is completely immersed under the liquid level of the absorption liquid, wherein the pressure is
I.e. by
. After the gas phase fully contacts the absorption liquid in the vacuum absorption tank 1, the residual phenol carried in the gas phase is dissolved in the absorption liquid and then led to a vacuum pump through a gas phase outlet 5, and the pressure at the gas phase outlet 5 is
I.e. by
. The operation avoids the phenol from damaging the stability of the vacuum system behind the vacuum absorption tank 1, and simultaneously avoids the hazardous chemical phenol from entering the vacuum pump to pollute the operation medium of the pump.
The liquid phase (i.e. absorption liquid) is injected into the vacuum absorption tank 1 through the liquid phase inlet 2 and then flows out of the tank body through the liquid phase outlet 3. The circulation flow of the absorption liquid between the vacuum absorption tank 1 and the absorption liquid tank 11 is realized by the liquid transfer pump 18. A gas phase balance pipe 12 is designed and installed between the vacuum absorption tank 1) and the absorption liquid tank 11, so that the gas phase pressure of the two tank bodies is the same, and the absorption liquid can be stably conveyed.
In addition, the absorption liquid is sampled periodically to detect the concentration of phenol, when the concentration of phenol is close to the saturation concentration of phenol, the phenol-containing absorption liquid in the absorption liquid tank 11 is emptied, and then new absorption liquid is supplemented, so that the effect of phenol absorption of the absorption liquid is ensured.
The process of adjusting the vacuum degree of the polycondensation reaction device 6 by the vacuum adjusting system in this embodiment is as follows:
the liquid level of the absorption liquid is adjusted by the opening degree of the flow regulating valve 10 at the liquid phase outlet 3 of the vacuum absorption tank 1, so that the vacuum degree of the polycondensation reaction device 6 is finely adjusted. Specifically, the pressure of the gas phase inlet 4 is adjusted by the hydraulic pressure formed by the height difference h between the outlet of the gas phase inlet 4 and the liquid level in the vacuum absorption tank 1.
Wherein the content of the first and second substances,
in order to increase the pressure in the polycondensation reaction apparatus 6,
the pressure of a gas phase outlet 5 of the vacuum absorption tank 1, rho is the density of absorption liquid, g is the gravity acceleration, and h is the height difference between a gas phase inlet 4 pipe outlet of the vacuum absorption tank 1 and the liquid level in the vacuum absorption tank 1.
Different pressure differences are generated by different absorption liquid level heights, and the embodiment takes ethylene glycol as the absorption liquid as an example, and specific numerical values refer to table 1. If the pressure P2101 at the gas-phase outlet 5 is kept constant, P1101 can be accurately regulated and controlled by FV-2101, so that the internal pressure of the polycondensation reaction device 6 can be effectively controlled.
TABLE 1 COMPARATIVE TABLE OF PRESSURE DIFFERENCE VALUES GENERATED BY VARIOUS LEVELS
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.
Claims (10)
1. A vacuum regulation method for a polycondensation reaction apparatus, characterized in that: a vacuum system is adopted, the vacuum system comprises a vacuum absorption tank (1) which is respectively communicated with the polycondensation reaction device (6) and a vacuum pump, and the vacuum degree in the polycondensation reaction device (6) is adjusted by controlling the liquid level height in the vacuum absorption tank (1).
2. The method of claim 1, wherein the vacuum system comprises: establish liquid phase import (2), liquid phase export (3), communicate gas phase import (4) of polycondensation reaction device (6) and the gas phase export (5) of intercommunication vacuum pump on vacuum absorption jar (1), liquid phase export (3) are higher than liquid phase import (2), gas phase import (4) and gas phase export (5) all are higher than liquid phase export (3), gas phase import (4) inwards extend along vacuum absorption jar (1) and form intake pipe (7), the exit end face of intake pipe (7) flushes with the bottom of liquid phase export (3).
3. The method of claim 2, wherein the vacuum system comprises: the liquid level in the vacuum absorption tank (1) is ensured to be higher than or equal to the outlet end surface of the air inlet pipe (7).
4. The method of claim 2, wherein the vacuum system comprises: an absorption liquid tank (11) is arranged to enable absorption liquid to circularly flow between the vacuum absorption tank (1) and the absorption liquid tank (11) along the liquid phase inlet (2) and the liquid phase outlet (3), and the flow of the absorption liquid at the liquid phase outlet (3) is adjusted according to the pressure at the gas phase outlet (5).
5. The method of claim 4, wherein the vacuum system comprises: the pressure of the gas-phase inlet (4) is controlled to be equal to the pressure in the polycondensation reaction device (6), and the pressure of the vacuum absorption tank (1) is controlled to be equal to the pressure of the absorption liquid tank (11).
6. The method of claim 4, wherein the vacuum system comprises: the boiling point of the absorption liquid is more than or equal to 130 ℃, and the absorption liquid is mutually soluble with the micromolecule compound contained in the gas phase generated by the polycondensation reaction but does not generate chemical reaction.
7. A vacuum system for a polycondensation reaction apparatus according to claim 2.
8. The vacuum system for a polycondensation reaction apparatus according to claim 7, wherein: the vacuum absorption tank (1) is provided with a pressure gauge (8), and a pipeline connected with the liquid phase outlet (3) is provided with a flow regulating valve (10).
9. The vacuum system for a polycondensation reaction apparatus according to claim 7, wherein: the liquid phase inlet (2) and the liquid phase outlet (3) are respectively communicated with the absorption liquid tank (11).
10. A vacuum system for a polycondensation reaction apparatus according to claim 9, wherein: a gas phase balance pipe (12) is arranged between the vacuum absorption tank (1) and the absorption liquid tank (11).
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