Continuous production equipment and production method for low-molecular-weight polyester

Abstract

The production equipment comprises a slurry tank, an esterification reactor, a multi-stage polycondensation tower and an esterification separation tower which are sequentially connected, the esterification separation tower is further circularly connected with the esterification reactor, the slurry tank is used for feeding alcohol and acid, the esterification reactor is used for carrying out esterification reaction, and the multi-stage polycondensation tower is connected with the esterification separation tower. The multi-stage polycondensation tower comprises multi-stage tower sections, the pressure of the multi-stage tower sections is gradually reduced from the feeding end to the discharging end, the multi-stage polycondensation tower is used for carrying out polycondensation reaction on esterification materials from the esterification reactor, polycondensation products generated by the multi-stage polycondensation tower are discharged, and the esterification separation tower is used for separating water, alcohol and small molecular substances in polycondensation condensate; and alcohol separated by the esterification separation tower flows back to the esterification reactor. The device can be used for continuous production of low-molecular-weight polyester, and can reduce equipment investment and separation energy consumption and reduce energy consumption and cost while improving efficiency and yield.

Description

Technical Field

[0001] The present application relates to the field of chemical engineering technology, and in particular to a continuous production device for low molecular weight polyester and a production method thereof. Background Art

[0002] Polyester is a polymer material widely used in textiles, plastic products and other industrial fields. The production methods of polyester can be divided into two types: intermittent production and continuous production. According to the molecular weight classification of polyester, polyester includes at least low molecular weight polyester and high molecular weight polyester. Most polyesters have a small output. Therefore, during production, the same production equipment often needs to be switched, resulting in intermittent operation of some low molecular weight polyesters. Intermittent production increases production time costs and reduces production efficiency. Summary of the invention

[0003] Based on this, it is necessary to provide a low molecular weight polyester continuous production equipment. The low molecular weight polyester continuous production equipment of the present invention can be used for the continuous production of low molecular weight polyester, while improving efficiency and output, reducing equipment investment and separation energy consumption, and reducing energy consumption and cost.

[0004] An embodiment of the present application provides a continuous production device for low molecular weight polyester.

[0005] A low molecular weight polyester continuous production equipment comprises a slurry tank, an esterification reactor, a multi-stage polycondensation tower and an esterification separation tower which are connected in sequence. The esterification separation tower is also cyclically connected to the esterification reactor to realize the reflux of alcohol separated by the esterification separation tower to the esterification reactor. The slurry tank is used to feed alcohol and acid. The esterification reactor is used to carry out esterification reaction. The multi-stage polycondensation tower comprises a plurality of tower sections. The pressure of the plurality of tower sections decreases step by step from the feed end to the discharge end. The multi-stage polycondensation tower is used to carry out polycondensation reaction on the esterification material from the esterification reactor and discharge the generated polycondensation product. The esterification separation tower is used to separate water, alcohol and small molecular substances in the polycondensation condensate after gas phase condensation from the multi-stage polycondensation tower.

[0006] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0007] (1) The slurry tank is connected to an alcohol raw material pipeline, and a flow meter is provided on the alcohol raw material pipeline;

[0008] (2) The slurry tank is connected to an acid feed bin.

[0009] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0010] (1) The low molecular weight polyester continuous production equipment further comprises a slurry pump and / or a material control valve, wherein the slurry pump and the material control valve are arranged on the slurry pipeline between the slurry tank and the esterification reactor;

[0011] (2) The low molecular weight polyester continuous production equipment also includes a cross heat exchanger, which is arranged on the slurry pipeline between the slurry tank and the esterification reactor. The discharge end of the multi-stage polycondensation tower is connected to the cross heat exchanger through a first heat exchange pipeline. The first heat exchange pipeline is provided with a first delivery pump to enable the cross heat exchanger to exchange heat between the condensation product produced by the multi-stage polycondensation tower and the slurry in the slurry pipeline.

[0012] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0013] (1) The esterification reactor is a horizontal reactor;

[0014] (2) The esterification reactor comprises a multi-stage reaction chamber, and adjacent reaction chambers are separated by partitions having overflow holes;

[0015] (3) The low molecular weight polyester continuous production equipment also includes a second heat exchange pipe, an external circulation heat exchanger and a second delivery pump. The second heat exchange pipe is located outside the esterification reactor and is connected to the circulation outlet and circulation inlet of the esterification reactor. The external circulation heat exchanger and the second delivery pump are respectively arranged on the second heat exchange pipe.

[0016] In some of the embodiments, the low molecular weight polyester continuous production equipment also includes an esterification material delivery pump, which is arranged on the esterification material delivery pipeline between the esterification reactor and the multi-stage condensation tower, and the esterification material delivery pipeline is also connected to a catalyst pipeline.

[0017] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0018] (1) The multi-stage tower sections of the multi-stage polycondensation tower are distributed along the vertical direction, wherein the feed end of the multi-stage polycondensation tower is located at the top and the discharge end is located at the bottom, and the pressure of the multi-stage tower sections decreases step by step from top to bottom;

[0019] (2) The operating pressure of the multi-stage tower sections of the multi-stage polycondensation tower is 5 KPaA~80 KPaA.

[0020] In some of the embodiments, the low molecular weight polyester continuous production equipment further comprises a plurality of sequentially connected condensers, wherein the plurality of condensers are connected to the polycondensation condensate conveying pipeline between the multi-stage polycondensation tower and the esterification separation tower.

[0021] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0022] (1) The gas outlet of the condenser of the next stage is connected to the condenser of the previous stage through the first circulation pipeline to realize the preheating of the circulating gas;

[0023] (2) The first-stage condenser is also connected to the multi-stage polycondensation tower through a second circulation pipeline to achieve partial gas phase reflux to the multi-stage polycondensation tower;

[0024] (3) A vacuum unit for realizing partial gas phase reflux and external discharge is connected to the second circulation pipeline of at least one stage of the condenser, and the vacuum unit is connected to the exhaust gas pipeline;

[0025] (4) A nitrogen pipeline for supplementing nitrogen is connected to the second circulation pipeline of at least one stage of the condenser, and the nitrogen pipeline is used to realize nitrogen stripping of the multi-stage polycondensation tower;

[0026] (5) A polycondensation condensate tank is connected to the position of the last stage condenser on the polycondensation condensate delivery pipeline;

[0027] (6) A polycondensation condensate pump is provided on the polycondensation condensate delivery pipeline.

[0028] In some embodiments, the low molecular weight polyester continuous production equipment also meets at least one of the following conditions:

[0029] (1) The gas outlet of the esterification reactor is also connected to the esterification separation tower;

[0030] (2) The gas outlet of the esterification separation tower is sequentially connected to the esterification tower top condenser and the esterification condensate tank, the gas outlet of the esterification tower top condenser is connected to the waste gas pipeline, the liquid outlet of the esterification tower top condenser is connected to the esterification condensate tank, and the esterification condensate tank is also connected to the waste water pipeline and the esterification separation tower to respectively realize the discharge and re-separation of the esterification condensate.

[0031] An embodiment of the present application also provides a method for continuous production of low molecular weight polyester.

[0032] A method for continuously producing low molecular weight polyester, using the above-mentioned continuous production equipment for low molecular weight polyester, comprises the following steps:

[0033] Adding alcohol and acid into a slurry tank, mixing and then conveying to an esterification reactor;

[0034] Controlling the esterification reactor to perform an esterification reaction to generate an esterified material;

[0035] Controlling the esterification materials and catalyst to enter the multi-stage polycondensation tower;

[0036] Controlling the multi-stage polycondensation tower to carry out polycondensation reaction on the esterification material from the esterification reactor, the polycondensation product produced by the multi-stage polycondensation tower is discharged, and the gas phase stripped by the multi-stage polycondensation tower is condensed to form a polycondensation condensate which enters the esterification separation tower; and

[0037] The esterification separation tower is controlled to separate water, alcohol and small molecular substances in the polycondensation condensate, and the alcohol separated by the esterification separation tower is refluxed to the esterification reactor for re-esterification circulation.

[0038] In some embodiments, the method for continuous production of low molecular weight polyester further satisfies at least one of the following conditions:

[0039] (1) The molar ratio of the alcohol to the acid is 1 to 1.5;

[0040] (2) The operating temperature of the slurry tank is 50°C~100°C;

[0041] (3) controlling the residence time of the reaction materials in each stage of the reaction chamber of the esterification reactor to be equal;

[0042] (4) controlling the pressure of the multi-stage tower sections of the multi-stage polycondensation tower to decrease step by step from 50 KPaA to 10 KPaA from the feed end to the discharge end;

[0043] (5) Control the operating temperature of the esterification reactor to 220°C~230°C

[0044] (6) Controlling the operating temperature of the multi-stage tower sections of the multi-stage polycondensation tower to be 225° C. to 235° C.

[0045] The above-mentioned low molecular weight polyester continuous production equipment can be used for the continuous production of low molecular weight polyester, and can reduce equipment investment and separation energy consumption, thereby reducing energy consumption and costs while improving efficiency and output. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0047] In order to more completely understand the present application and its beneficial effects, the following description will be given in conjunction with the accompanying drawings. In the following description, the same reference numerals represent the same parts.

[0048] FIG1 is a schematic diagram of a continuous production device for low molecular weight polyester according to an embodiment of the present invention.

[0049] Description of Reference Numerals

[0050] 10. Low molecular weight polyester continuous production equipment; 100. Slurry tank; 200. Esterification reactor; 300. Multi-stage polycondensation tower; 400. Esterification separation tower; 500. Acid feed bin; 600. Slurry pump; 700. Material control valve; 800. Cross heat exchanger; 900. External circulation heat exchanger; 1010. First delivery pump; 1020. Second delivery pump; 1100. Esterification material delivery pump; 1110. Primary condenser; 1120. Secondary condenser; 1200. Vacuum unit; 1300. Polycondensation condensate tank; 140 0. Polycondensation condensate pump; 1500. Esterification tower top condenser; 1600. Esterification condensate tank; 1700. Valve assembly; 1800. Esterification condensate pump; 101. Alcohol raw material pipeline; 102. Slurry pipeline; 103. Esterification material conveying pipeline; 104. Catalyst pipeline; 1051. First heat exchange pipeline; 1052. Second heat exchange pipeline; 106. Polycondensation condensate conveying pipeline; 1071. First circulation pipeline; 1072. Second circulation pipeline; 108. Nitrogen pipeline; 109. Waste gas pipeline; 1011. Wastewater pipeline. DETAILED DESCRIPTION

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0052] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0053] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0055] In the description of the present invention, "several" means more than one, "many" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0056] In this article, "optionally", "optional", "optional" means optional, that is, it means to be selected from any of the two parallel solutions of "yes" or "no". If there are multiple "optional" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent. In this application, the descriptions such as "optionally contain" and "optionally include" mean "contain or not contain".

[0057] In the present application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to an integer in the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints, which is equivalent to directly listing each integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. In other words, unless otherwise specified, the numerical range disclosed in the present application should be understood to include any and all sub-ranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for a broad range of quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0059] The embodiment of the present application provides a low molecular weight polyester continuous production device 10 to solve the problem that some low molecular weight polyesters in the prior art are produced in intermittent operation, which increases the production time cost and reduces the production efficiency. The low molecular weight polyester continuous production device 10 will be described below in conjunction with the accompanying drawings.

[0060] The low molecular weight polyester continuous production equipment 10 provided in the embodiment of the present application is exemplified as shown in Figure 1, which is a structural schematic diagram of the low molecular weight polyester continuous production equipment 10 provided in the embodiment of the present application. The low molecular weight polyester continuous production equipment 10 of the present application can be used for the continuous production of low molecular weight polyester.

[0061] In order to more clearly illustrate the structure of the low molecular weight polyester continuous production equipment 10, the low molecular weight polyester continuous production equipment 10 will be introduced below with reference to the accompanying drawings.

[0062] For example, please refer to FIG. 1 , a low molecular weight polyester continuous production equipment 10 includes a slurry tank 100, an esterification reactor 200, a multi-stage polycondensation tower 300 and an esterification separation tower 400 connected in sequence. The esterification separation tower 400 is also connected to the esterification reactor 200 in a loop so that the alcohol separated by the esterification separation tower 400 can be refluxed to the esterification reactor 200. The slurry tank 100 is used to feed alcohol and acid. The esterification reactor 200 is used to perform an esterification reaction. The multi-stage polycondensation tower 300 includes a multi-stage tower section. The pressure of the multi-stage tower section decreases step by step from the feed end to the discharge end. The multi-stage polycondensation tower 300 is used to perform a polycondensation reaction on the esterification material from the esterification reactor 200. The polycondensation product produced by the multi-stage polycondensation tower 300 is discharged. The esterification separation tower 400 is used to separate water, alcohol, and small molecular substances from the polycondensation condensate formed after the gas phase from the multi-stage polycondensation tower 300 is condensed. The function of the esterification separation tower 400 is to remove the water and small molecules produced by esterification and polycondensation to break the reaction balance in the esterification reactor 200 and the multi-stage polycondensation tower 300 and promote the forward reaction.

[0063] The above-mentioned low molecular weight polyester continuous production equipment 10 can be used for the continuous production of low molecular weight polyester, and can reduce equipment investment and separation energy consumption, thereby reducing costs while improving efficiency and output.

[0064] The above-mentioned low molecular weight polyester continuous production equipment 10 can realize the continuous production of low molecular weight polyester. Compared with traditional intermittent production, continuous production has many advantages: (1) Improve efficiency and output: In continuous production, reactors, separators and other equipment are connected in series to form a production line, and materials flow from one unit to the next unit, realizing automated and unmanned continuous operation. This can greatly reduce the preparation time between batches, improve the overall efficiency of production, and realize large-scale batch production. (2) Reduce energy consumption and cost: Continuous production can better utilize heat and other energy by optimizing process design and operating parameters, thereby significantly reducing the energy consumption per unit product under the premise of producing the same number of products. In addition, due to the reduction of equipment and labor input, the production cost is also reduced accordingly. (3) Improve the uniformity and stability of product quality: In continuous production, materials go through a series of continuous processes, and each stage has strict process control, which helps to maintain the consistency and stability of product performance. Compared with the batch differences in intermittent production, the quality of continuous production products is more uniform and controllable. (4) Easy to automate and intelligently manage: Continuous production lines are usually equipped with advanced sensors, control systems, and automatic adjustment equipment. These technologies can monitor the production process in real time and quickly adjust parameters to cope with changes, thereby improving product output and quality. In summary, the continuous production method can improve production efficiency, reduce costs, and ensure the consistency and stability of product quality for the manufacture of polyester and other chemical products.

[0065] In some embodiments, the slurry tank 100 is connected to an alcohol raw material pipeline 101, and a flow meter is provided on the alcohol raw material pipeline 101. Preferably, a pump and a valve may also be provided on the alcohol raw material pipeline 101.

[0066] In some of the embodiments, the slurry tank 100 is connected to an acid feed tank 500 .

[0067] In some of the embodiments, please refer to Figure 1, the low molecular weight polyester continuous production equipment 10 also includes a slurry pump 600 and / or a material control valve 700, and the slurry pump 600 and the material control valve 700 are arranged on the slurry pipeline 102 between the slurry tank 100 and the esterification reactor 200.

[0068] In some embodiments, the low molecular weight polyester continuous production equipment 10 further includes a cross heat exchanger 800. The cross heat exchanger 800 is disposed on the slurry pipeline 102 between the slurry tank 100 and the esterification reactor 200. The discharge end of the multi-stage polycondensation tower 300 is connected to the cross heat exchanger 800 through the first heat exchange pipeline 1051, so that the cross heat exchanger 800 performs heat exchange between the polycondensation product produced by the multi-stage polycondensation tower 300 and the slurry in the slurry pipeline 102.

[0069] In some of the embodiments, please refer to FIG. 1 , a first delivery pump 1010 is disposed on the first heat exchange pipe 1051 .

[0070] In some embodiments, the esterification reactor 200 is a horizontal reactor. It should be noted that, as shown in FIG1 , in the present application, the multi-stage reaction chambers of the horizontal reactor are distributed along the horizontal direction, and correspondingly, the multi-stage tower sections of the multi-stage polycondensation tower 300 are distributed along the vertical direction.

[0071] In some embodiments, the esterification reactor 200 includes a multi-stage reaction chamber. Adjacent reaction chambers are separated by a partition having overflow holes. The size and number of the overflow holes on the partition can be set according to actual needs.

[0072] Preferably, in some of the embodiments, the esterification reactor 200 includes 3 to 5 reaction chambers.

[0073] In some embodiments, the low molecular weight polyester continuous production equipment 10 further includes a second heat exchange pipe 1052, an external circulation heat exchanger 900 and a second delivery pump 1020. The second heat exchange pipe 1052 is located outside the esterification reactor 200 and is connected to the circulation outlet and the circulation inlet of the esterification reactor 200, and the external circulation heat exchanger 900 and the second delivery pump 1020 are respectively arranged on the second heat exchange pipe 1052.

[0074] In some embodiments, as shown in FIG1 , the low molecular weight polyester continuous production equipment 10 further includes an esterification material delivery pump 1100. The esterification material delivery pump 1100 is disposed on an esterification material delivery pipeline 103 between the esterification reactor 200 and the multi-stage polycondensation tower 300, and the esterification material delivery pipeline 103 is also connected to a catalyst pipeline 104.

[0075] In some of the embodiments, the multi-stage tower sections of the multi-stage condensation tower 300 are distributed along the vertical direction, wherein the feed end of the multi-stage condensation tower 300 is located at the top and the discharge end is located at the bottom, and the pressure of the multi-stage tower sections decreases step by step from top to bottom.

[0076] In some embodiments, as shown in Fig. 1, the multi-stage tower sections of the multi-stage polycondensation tower 300 are respectively connected in parallel to the polycondensation condensate delivery pipeline 106. Valve assemblies 1700 are respectively provided on the pipelines connecting the tower sections of each stage and the polycondensation condensate delivery pipeline 106.

[0077] In some of the embodiments, the operating pressure of the multi-stage tower section of the multi-stage polycondensation tower 300 is 5 KPaA-80 KPaA. In one specific example, the operating pressure of the multi-stage tower section is different.

[0078] In some embodiments, the low molecular weight polyester continuous production equipment 10 further includes a multi-stage sequentially connected condenser connected to the polycondensation condensate conveying pipeline 106 between the multi-stage polycondensation tower 300 and the esterification separation tower 400 .

[0079] Preferably, there may be a plurality of condensers, and the plurality of condensers respectively form a primary condenser 1110, a secondary condenser 1120, etc. Please refer to Fig. 1, which shows a two-stage condenser.

[0080] In some of the embodiments, the gas outlet of the latter stage condenser is cyclically connected to the former stage condenser through the first circulation pipe 1071 to achieve circulating gas preheating.

[0081] In some of the embodiments, the first-stage condenser is further connected to the multi-stage polycondensation tower 300 via the second circulation pipeline 1072 to achieve partial gas phase reflux to the multi-stage polycondensation tower 300 .

[0082] In some of the embodiments, a vacuum unit 1200 for realizing partial gas phase reflux and external discharge is connected to the first circulation pipeline 1071 of at least one primary condenser, and the vacuum unit 1200 is connected to the exhaust gas pipeline 109 .

[0083] In some embodiments, a nitrogen pipeline 108 for supplementing nitrogen is connected to the first circulation pipeline 1071 of at least one stage condenser. The nitrogen pipeline 108 is used to realize nitrogen stripping of the multi-stage polycondensation tower 300. Preferably, in the present application, nitrogen can be used when stripping is performed in the multi-stage polycondensation tower 300.

[0084] In some of the embodiments, a polycondensation condensate tank 1300 is connected to the polycondensation condensate delivery pipeline 106 at the position of the last stage condenser.

[0085] In some of the embodiments, please refer to FIG. 1 , a polycondensate pump 1400 is disposed on the polycondensate delivery pipeline 106 .

[0086] In some embodiments, the gas outlet of the esterification reactor 200 is also connected to the esterification separation tower 400, so that the water, alcohol, small molecule substances, and tetrahydrofuran components of the esterification separation tower 400 enter the esterification separation tower 400 through the gas outlet to be separated.

[0087] In some of the embodiments, the gas outlet of the esterification separation tower 400 is sequentially connected to the esterification tower top condenser 1500 and the esterification condensate tank 1600, the gas outlet of the esterification tower top condenser 1500 is connected to the exhaust gas pipeline 109, the liquid outlet of the esterification tower top condenser 1500 is connected to the esterification condensate tank 1600, and the esterification condensate tank 1600 is also connected to the wastewater pipeline 1011 and the esterification separation tower 400 to respectively realize the discharge and re-separation of the esterification condensate.

[0088] In some of the embodiments, the esterification condensate tank 1600 is connected to the wastewater pipeline 1011 and the esterification separation tower 400 via the esterification condensate pump 1800 .

[0089] Preferably, a material control valve 700 may also be provided on the pipeline between the esterification condensate pump 1800 and the esterification separation tower 400 .

[0090] In some embodiments, a valve assembly 1700 is provided on the exhaust pipe 109. The valve assembly 1700 can be set to a corresponding type according to actual needs. For example, the valve assembly 1700 can be a manual valve or a solenoid valve. Preferably, the valve assembly 1700 is a solenoid valve to achieve automatic control.

[0091] An embodiment of the present application also provides a method for continuous production of low molecular weight polyester.

[0092] It should be noted that, in this article, unless otherwise specified, each reaction step can be carried out in the order described herein, or can be carried out in a non-sequential manner. For example, other steps may be included between each reaction step, and the order of the reaction steps may also be appropriately swapped. This can be determined by the technician based on conventional knowledge and experience. Preferably, the reaction method herein is carried out sequentially.

[0093] A method for continuously producing low molecular weight polyester, using the above-mentioned low molecular weight polyester continuous production equipment 10, comprises the following steps:

[0094] Please refer to FIG. 1 , alcohol and acid are added into a slurry tank 100 , mixed, and then transported to an esterification reactor 200 .

[0095] The esterification reactor 200 is controlled to perform an esterification reaction to generate an esterified material.

[0096] The esterification materials and catalyst are controlled to enter the multi-stage polycondensation tower 300.

[0097] The multi-stage polycondensation tower 300 is controlled to perform polycondensation reaction on the esterification material from the esterification reactor 200, and the polycondensation product produced by the multi-stage polycondensation tower 300 is discharged. The gas phase stripped by the multi-stage polycondensation tower 300 is condensed to form a polycondensation condensate which enters the esterification separation tower 400.

[0098] The esterification separation tower 400 is controlled to separate water, alcohol and small molecular substances in the polycondensation condensate, and the alcohol separated by the esterification separation tower 400 is refluxed to the esterification reactor 200 for re-esterification circulation.

[0099] In some embodiments, the method further comprises the following step: water, alcohol, small molecule substances, and tetrahydrofuran in the esterification separation tower 400 enter the esterification separation tower 400 to be separated respectively.

[0100] In some embodiments, the molar ratio of alcohol to acid is 1 to 1.5. The molar ratio of alcohol to acid can be set according to actual needs, for example, the molar ratio of alcohol to acid is 1, and for another example, the molar ratio of alcohol to acid is 1.5. It is not difficult to understand that in other examples, the molar ratio of alcohol to acid can also be other ratios.

[0101] In some of the embodiments, the operating temperature of the slurry tank 100 is 50°C to 100°C. Preferably, the operating temperature of the slurry tank 100 is 60°C to 85°C.

[0102] In some embodiments, the residence time of the reaction materials in each stage reaction chamber of the esterification reactor 200 is controlled to be equal.

[0103] In some of the embodiments, the pressure of the multi-stage tower section of the multi-stage polycondensation tower 300 is controlled to decrease step by step from 50 KPaA to 10 KPaA from the feed end to the discharge end.

[0104] In some embodiments, the operating temperature of the esterification reactor 200 is controlled to be 220° C.-230° C.

[0105] In some of the embodiments, the operating temperature of the multi-stage tower section of the multi-stage polycondensation tower 300 is controlled to be 225° C. to 235° C.

[0106] In some embodiments, the catalyst includes one or more of p-toluenesulfonic acid, tetrabutyl titanate, and zinc acetate. The role of the catalyst is to accelerate the polycondensation reaction and improve the reaction efficiency.

[0107] It should be noted that low molecular weight polyester refers to polyester materials with relatively low molecular weight, and its number average molecular weight (Mn) is usually less than 10,000. Due to its low molecular weight, low molecular weight polyesters often exhibit different physical and chemical properties from high molecular weight polyesters, such as lower melting point, better solubility and higher reactivity. The characteristics of low molecular weight polyesters include (1) Biodegradability: Low molecular weight polyesters have good biodegradability, which helps to reduce environmental pollution. (2) Thermoplasticity: Low molecular weight polyester materials can usually be reshaped after heating, which is convenient for recycling. (3) Chemical modification: Chemical modification can improve or give low molecular weight polyesters new properties, such as improving heat resistance and increasing flexibility. (4) Solubility: Low molecular weight polyesters usually have better solubility and are easy to mix with other materials to form composite materials.

[0108] The main types of low molecular weight polyesters include: (1) Polyethylene terephthalate (PET), used as adhesives, coating materials, plasticizers, etc. Polyethylene terephthalate has good transparency and mechanical properties, but when the molecular weight is low, its melting point and glass transition temperature will decrease. (2) Polybutylene succinate (PBS): used to produce environmentally friendly products such as degradable plastic bags and tableware. Polybutylene succinate has good biodegradability and can be decomposed in the natural environment, which is environmentally friendly. (3) Polybutylene adipate (PBA): used as biomedical materials, such as drug sustained release carriers, tissue engineering scaffolds, etc. Polybutylene adipate has good biocompatibility and biodegradability. (4) Polybutylene suberate (PBSub): suitable for occasions requiring higher thermal stability, such as adhesives and coatings at high temperatures. Polybutylene suberate has good crystallinity and heat resistance. (5) Low molecular weight forms of polylactic acid (PLA): used in biomedical materials, food packaging, agricultural mulch, etc. Polylactic acid has good biodegradability and good mechanical and processing properties. (6) Aliphatic polyesters: widely used in drug sustained-release systems, tissue engineering, cosmetics and personal care products, etc. Aliphatic polyesters have good biocompatibility and biodegradability, and their properties can be further optimized through chemical modification.

[0109] In some of the embodiments, the acid in the present application includes a dibasic acid. For example, the acid in the present application includes one or more of terephthalic acid (TPA), adipic acid, succinic acid, sebacic acid, and isophthalic acid. Among them, terephthalic acid (TPA) is widely used to prepare polyethylene terephthalate (PET). Adipic acid is used to prepare nylon 66 and low molecular weight polyester. Succinic acid is used to prepare polybutylene succinate (PBS). Sebacic acid is used to prepare biodegradable polyester. Isophthalic acid is used to prepare polyester with special properties, such as improving heat resistance and chemical stability.

[0110] In some of the embodiments, the alcohol in the present application includes a diol. For example, the alcohol in the present application includes one or more of ethylene glycol, butanediol, propylene glycol, neopentyl glycol, and diethylene glycol. Among them, ethylene glycol is widely used in the preparation of PET. Butanediol is used to prepare PBS and other low molecular weight polyesters. Propylene glycol is used to prepare polyesters with special properties, such as improving biocompatibility. Neopentyl glycol is used to prepare polyesters with high heat resistance and chemical resistance. Diethylene glycol is used to prepare polyesters with specific properties, such as improving flexibility.

[0111] The continuous production method of low molecular weight polyester of the present application includes batching, separation, esterification, polycondensation and other stages. Specifically, during the batching process, alcohol and acid enter the slurry tank 100 in a certain ratio for continuous slurrying, and the temperature is generally between 50°C and 100°C; the slurry enters the esterification reactor 200 through the cross heat exchanger 800 for esterification reaction. The esterification reaction and polycondensation reaction are multi-stage reactions. According to the characteristics of the multi-stage reaction, the closer the esterification reactor 200 and the multi-stage polycondensation tower 300 are to the plug flow, the shorter the required residence time. Based on this, in the present application, the esterification stage of this design adopts a horizontal multi-chamber esterification reactor 200, and the number of reaction chambers is generally 3 to 5. The esterification separation tower 400 separates water, alcohol, and small molecular substances, and the esterification separation tower 400 obtains alcohol with a high concentration, which is then refluxed to the first-stage reaction chamber of the esterification reactor 200, which is conducive to the recycling of alcohol, and the recycled alcohol increases the alcohol-acid ratio in the esterification reactor 200, thereby promoting the esterification reaction rate. The esterified material of the esterification reactor 200 enters the multi-stage polycondensation tower 300 through the esterification material delivery pump 1100 and mixed with the catalyst. Each tower section of the multi-stage polycondensation tower 300 has a different operating pressure. This design enables the alcohol in the esterified material to enter the multi-stage polycondensation tower 300, and the alcohol in the liquid phase will not be instantly drawn away in large quantities, thereby avoiding affecting the product molecular weight and molecular weight distribution.

[0112] Example 1

[0113] This embodiment provides a low molecular weight polyester continuous production device 10.

[0114] Please refer to Figure 1, the low molecular weight polyester continuous production equipment 10 of this embodiment includes a slurry tank 100, an esterification reactor 200, a multi-stage condensation tower 300, an esterification separation tower 400, a slurry pump 600, a material control valve 700, a cross heat exchanger 800, an external circulation heat exchanger 900, a first delivery pump 1010, a second delivery pump 1020, an esterification material delivery pump 1100, a primary condenser 1110, a secondary condenser 1120, an esterification tower top condenser 1500 and an esterification condensate tank 1600 connected in sequence.

[0115] The slurry tank 100 is connected to an alcohol raw material pipeline 101, and a flow meter is arranged on the alcohol raw material pipeline 101. The slurry tank 100 is connected to an acid feed bin 500. A slurry pump 600 and a material control valve 700 are arranged on the slurry pipeline 102 between the slurry tank 100 and the esterification reactor 200. A cross heat exchanger 800 is arranged on the slurry pipeline 102 between the slurry tank 100 and the esterification reactor 200.

[0116] The esterification reactor 200 is a horizontal reactor. The esterification reactor 200 includes three stages of reaction chambers, and adjacent reaction chambers are separated by a partition with overflow holes. The esterification separation tower 400 is also connected to the esterification reactor 200 in a loop. The second heat exchange pipeline 1052 is located outside the esterification reactor 200 and is connected to the circulation outlet and circulation inlet of the esterification reactor 200. The external circulation heat exchanger 900 and the second delivery pump 1020 are respectively arranged on the second heat exchange pipeline 1052. The esterification material delivery pump 1100 is arranged on the esterification material delivery pipeline 103 between the esterification reactor 200 and the multi-stage polycondensation tower 300, and the esterification material delivery pipeline 103 is also connected to the catalyst pipeline 104. The gas outlet of the esterification reactor 200 is also connected to the esterification separation tower 400.

[0117] The multi-stage polycondensation tower 300 includes four tower sections. The multi-stage tower sections of the multi-stage polycondensation tower 300 are distributed along the vertical direction, wherein the feed end of the multi-stage polycondensation tower 300 is located at the top and the discharge end is located at the bottom.

[0118] The discharge end of the multi-stage polycondensation tower 300 is connected to the cross heat exchanger 800 through the first heat exchange pipe 1051, so that the cross heat exchanger 800 can exchange heat between the polycondensation product produced by the multi-stage polycondensation tower 300 and the slurry in the slurry pipe 102. The first heat exchange pipe 1051 is provided with a first delivery pump 1010.

[0119] The primary condenser 1110 and the secondary condenser 1120 are sequentially connected to the polycondensation condensate delivery pipeline 106 between the multi-stage polycondensation tower 300 and the esterification separation tower 400. The gas outlet of the secondary condenser 1120 is circulated and connected to the primary condenser 1110 through the first circulation pipeline 1071 to realize the preheating of the circulating gas. The function of the primary condenser 1110 is to exchange heat between the reflux gas and the gas phase to be condensed to achieve energy saving. The first circulation pipeline 1071 of the secondary condenser 1120 is connected to a vacuum unit 1200 for realizing partial gas phase reflux and external discharge, and the vacuum unit 1200 is connected to the exhaust gas pipeline 109. The first circulation pipeline 1071 of the secondary condenser 1120 is connected to a nitrogen pipeline 108 for supplementing nitrogen. The primary condenser 1110 is also connected to the multi-stage polycondensation tower 300 through the second circulation pipeline 1072 to realize partial gas phase reflux to the multi-stage polycondensation tower 300. The polycondensation condensate delivery pipeline 106 is connected to a polycondensation condensate tank 1300 at a position of the secondary condenser 1120. The polycondensation condensate delivery pipeline 106 is provided with a polycondensation condensate pump 1400.

[0120] The gas outlet of the esterification separation tower 400 is sequentially connected to the esterification tower top condenser 1500 and the esterification condensate tank 1600, the gas outlet of the esterification tower top condenser 1500 is connected to the exhaust gas pipeline 109, the liquid outlet of the esterification tower top condenser 1500 is connected to the esterification condensate tank 1600, and the esterification condensate tank 1600 is also connected to the wastewater pipeline 1011 and the esterification separation tower 400 to respectively realize the discharge and re-separation of the esterification condensate.

[0121] Example 2

[0122] This embodiment provides a method for continuous production of low molecular weight polyester.

[0123] The method for continuous production of low molecular weight polyester in this embodiment adopts the low molecular weight polyester continuous production equipment 10 of embodiment 1, and comprises the following steps:

[0124] 1,4-Butanediol and adipic acid in a molar ratio of 1.3 are added into the slurry tank 100 for mixing. The operating temperature of the slurry tank 100 is 60° C. The mixed material is transported to the esterification reactor 200 .

[0125] The residence time of the mixed material in the three-stage reaction chamber of the esterification reactor 200 is 3 hours. The operating temperature of the esterification reactor 200 is 220° C. The esterification reactor 200 is controlled to perform an esterification reaction to generate an esterified material.

[0126] The esterification materials and catalysts are controlled to enter the multi-stage polycondensation tower 300, and the pressure of the four-stage tower section of the multi-stage polycondensation tower 300 is controlled to be 50KPaA, 40KPaA, 30KPaA, and 10KPaA from the feed end to the discharge end. The residence time of the esterification materials in the four-stage tower section is 3h, 3h, 2h, and 1h respectively. The operating temperature of the multi-stage tower section of the multi-stage polycondensation tower 300 is controlled to be 225°C. The multi-stage polycondensation tower 300 is controlled to perform a polycondensation reaction on the esterification materials from the esterification reactor 200, and the polycondensation products produced by the multi-stage polycondensation tower 300 are discharged after heat exchange in the cross heat exchanger 800, and the gas phase stripped by the multi-stage polycondensation tower 300 is condensed to form a polycondensation condensate and enter the esterification separation tower 400.

[0127] The esterification separation tower 400 is controlled to separate water, alcohol and small molecular substances in the polycondensation condensate, and the alcohol separated by the esterification separation tower 400 is refluxed to the esterification reactor 200 for re-esterification circulation.

[0128] The hydroxyl value of the finally obtained esterification material is 105, and the acid value is 15. The hydroxyl value of the polycondensation product is 56, and the acid value is 0.16. The molecular weight of the polycondensation product is 2000.

[0129] Example 3

[0130] This embodiment provides a method for continuous production of low molecular weight polyester.

[0131] The low molecular weight polyester continuous production method of this embodiment adopts the low molecular weight polyester continuous production equipment 10 which is substantially the same as that of the embodiment 1, except that, in this embodiment, the esterification reactor 200 of the low molecular weight polyester continuous production equipment 10 includes a four-stage reaction chamber, and the multi-stage polycondensation tower 300 includes a five-stage tower section, and includes the following steps:

[0132] 1,6-hexanediol and adipic acid at a molar ratio of 1.06 are added to the slurry tank 100 for mixing. The operating temperature of the slurry tank 100 is 60° C. The mixed material is transported to the esterification reactor 200 .

[0133] The residence time of the mixed material in the four-stage reaction chamber of the esterification reactor 200 is 5h, 3h, 3h, and 3h respectively. The operating temperature of the esterification reactor 200 is 230° C. The esterification reactor 200 is controlled to perform an esterification reaction to generate an esterified material.

[0134] The esterification materials and catalysts are controlled to enter the multi-stage polycondensation tower 300, and the pressure of the five-stage tower section of the multi-stage polycondensation tower 300 is controlled to be 50KPaA, 30KPaA, 20KPaA, 15KPaA, and 10KPaA from the feed end to the discharge end. The residence time of the esterification materials in the five-stage tower section is 5h, 3h, 3h, 2h, and 1h respectively. The operating temperature of the multi-stage tower section of the multi-stage polycondensation tower 300 is controlled to be 235°C. The multi-stage polycondensation tower 300 is controlled to perform polycondensation reaction on the esterification materials from the esterification reactor 200, and the polycondensation products produced by the multi-stage polycondensation tower 300 are discharged after heat exchange in the cross heat exchanger 800, and the gas phase stripped by the multi-stage polycondensation tower 300 is condensed to form a polycondensation condensate and enter the esterification separation tower 400.

[0135] The esterification separation tower 400 is controlled to separate water, alcohol and small molecular substances in the polycondensation condensate, and the alcohol separated by the esterification separation tower 400 is refluxed to the esterification reactor 200 for re-esterification circulation.

[0136] The hydroxyl value of the finally obtained esterification material is 38, and the acid value is 8. The hydroxyl value of the polycondensation product is 28.6, and the acid value is 0.18. The molecular weight of the polycondensation product is 4000.

[0137] Based on Example 1 and Example 2, it can be seen that the low molecular weight polyester continuous production equipment 10 of the present application can be used for the continuous production of low molecular weight polyester.

[0138] In summary, the low molecular weight polyester continuous production equipment 10 of the present invention has the following beneficial effects:

[0139] (1) According to the characteristics of polyester reaction kinetics, the esterification reactor 200 and the multi-stage polycondensation tower 300 are designed to be close to the plug flow state. At the same time, the esterification separation tower 400 is used to continuously remove water, small molecules and other substances to promote the forward reaction, shorten the residence time required for the reaction, and reduce equipment investment.

[0140] (2) The alcohol removed with the gas phase during the esterification and polycondensation process is simply separated by an esterification separation tower 400, and the alcohol-containing material in the esterification separation tower 400 is refluxed to the first-stage reaction chamber of the esterification reactor 200 to promote the reaction and reduce energy consumption.

[0141] (3) Each stage of the multi-stage polycondensation tower 300 uses a different operating pressure, and the pressure of the tower section is reduced step by step, so that the molecular weight of the produced product can be controlled.

[0142] (4) The nitrogen used for stripping in the multi-stage polycondensation tower 300 can be recycled, saving material consumption.

[0143] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0144] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0145] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A low molecular weight polyester continuous production equipment, characterized in that: The invention comprises a slurry tank, an esterification reactor, a multi-stage polycondensation tower and an esterification separation tower which are connected in sequence. The esterification separation tower is also cyclically connected to the esterification reactor so that the alcohol separated by the esterification separation tower can be refluxed to the esterification reactor. The slurry tank is used to feed alcohol and acid. The esterification reactor is used to carry out esterification reaction. The multi-stage polycondensation tower comprises multi-stage tower sections. The pressure of the multi-stage tower sections is gradually reduced from the feed end to the discharge end. The multi-stage polycondensation tower is used to carry out polycondensation reaction on the esterification material from the esterification reactor and discharge the generated polycondensation product. The esterification separation tower is used to separate water, alcohol and small molecular substances in the polycondensation condensate after gas phase condensation from the multi-stage polycondensation tower.

2. The low molecular weight polyester continuous production equipment according to claim 1, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The slurry tank is connected to an alcohol raw material pipeline, and a flow meter is provided on the alcohol raw material pipeline; (2) The slurry tank is connected to an acid feed bin.

3. The low molecular weight polyester continuous production equipment according to claim 1, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The low molecular weight polyester continuous production equipment further comprises a slurry pump and / or a material control valve, wherein the slurry pump and the material control valve are arranged on the slurry pipeline between the slurry tank and the esterification reactor; (2) The low molecular weight polyester continuous production equipment also includes a cross heat exchanger, which is arranged on the slurry pipeline between the slurry tank and the esterification reactor. The discharge end of the multi-stage polycondensation tower is connected to the cross heat exchanger through a first heat exchange pipeline. The first heat exchange pipeline is provided with a first delivery pump to enable the cross heat exchanger to exchange heat between the condensation product produced by the multi-stage polycondensation tower and the slurry in the slurry pipeline.

4. The low molecular weight polyester continuous production equipment according to claim 1, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The esterification reactor is a horizontal reactor; (2) The esterification reactor comprises a multi-stage reaction chamber, and adjacent reaction chambers are separated by partitions having overflow holes; (3) The low molecular weight polyester continuous production equipment also includes a second heat exchange pipe, an external circulation heat exchanger and a second delivery pump. The second heat exchange pipe is located outside the esterification reactor and is connected to the circulation outlet and circulation inlet of the esterification reactor. The external circulation heat exchanger and the second delivery pump are respectively arranged on the second heat exchange pipe.

5. The low molecular weight polyester continuous production equipment according to any one of claims 1 to 4, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The low molecular weight polyester continuous production equipment further comprises an esterification material delivery pump, which is arranged on an esterification material delivery pipeline between the esterification reactor and the multi-stage polycondensation tower, and the esterification material delivery pipeline is also connected to a catalyst pipeline; (2) The multi-stage tower sections of the multi-stage polycondensation tower are distributed along the vertical direction, wherein the feed end of the multi-stage polycondensation tower is located at the top and the discharge end is located at the bottom, and the pressure of the multi-stage tower sections decreases step by step from top to bottom; (3) The operating pressure of the multi-stage tower sections of the multi-stage polycondensation tower is 5 KPaA~80 KPaA.

6. The low molecular weight polyester continuous production equipment according to any one of claims 1 to 4, characterized in that: The low molecular weight polyester continuous production equipment also includes a multi-stage condenser connected in sequence, and the multi-stage condenser is connected to the polycondensation condensate conveying pipeline between the multi-stage polycondensation tower and the esterification separation tower.

7. The low molecular weight polyester continuous production equipment according to claim 6, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The gas outlet of the condenser of the next stage is connected to the condenser of the previous stage through the first circulation pipeline to realize the preheating of the circulating gas; (2) The first-stage condenser is also connected to the multi-stage polycondensation tower through a second circulation pipeline to achieve partial gas phase reflux to the multi-stage polycondensation tower; (3) A vacuum unit for realizing partial gas phase reflux and external discharge is connected to the first circulation pipeline of at least one stage of the condenser, and the vacuum unit is connected to the exhaust gas pipeline; (4) A nitrogen pipeline for supplementing nitrogen is connected to the first circulation pipeline of at least one stage of the condenser, and the nitrogen pipeline is used to realize nitrogen stripping of the multi-stage polycondensation tower; (5) A polycondensation condensate tank is connected to the position of the last stage condenser on the polycondensation condensate delivery pipeline; (6) A polycondensation condensate pump is provided on the polycondensation condensate delivery pipeline.

8. The low molecular weight polyester continuous production equipment according to any one of claims 1 to 4 and 7, characterized in that: The low molecular weight polyester continuous production equipment also meets at least one of the following conditions: (1) The gas outlet of the esterification reactor is also connected to the esterification separation tower; (2) The gas outlet of the esterification separation tower is sequentially connected to the esterification tower top condenser and the esterification condensate tank, the gas outlet of the esterification tower top condenser is connected to the waste gas pipeline, the liquid outlet of the esterification tower top condenser is connected to the esterification condensate tank, and the esterification condensate tank is also connected to the waste water pipeline and the esterification separation tower to respectively realize the discharge and re-separation of the esterification condensate.

9. A method for continuous production of low molecular weight polyester, characterized in that: The low molecular weight polyester continuous production equipment according to any one of claims 1 to 8 comprises the following steps: Adding alcohol and acid into a slurry tank, mixing and then conveying to an esterification reactor; Controlling the esterification reactor to perform an esterification reaction to generate an esterified material; Controlling the esterification materials and catalyst to enter the multi-stage polycondensation tower; Controlling the multi-stage polycondensation tower to carry out polycondensation reaction on the esterification material from the esterification reactor, the polycondensation product produced by the multi-stage polycondensation tower is discharged, and the gas phase stripped by the multi-stage polycondensation tower is condensed to form a polycondensation condensate which enters the esterification separation tower; as well as The esterification separation tower is controlled to separate water, alcohol and small molecular substances in the polycondensation condensate, and the alcohol separated by the esterification separation tower is refluxed to the esterification reactor for re-esterification circulation.

10. The method for continuous production of low molecular weight polyester according to claim 9, characterized in that: The continuous production method of low molecular weight polyester also meets at least one of the following conditions: (1) The molar ratio of the alcohol to the acid is 1 to 1.5; (2) The operating temperature of the slurry tank is 50°C~100°C; (3) controlling the residence time of the reaction materials in each stage of the reaction chamber of the esterification reactor to be equal; (4) controlling the pressure of the multi-stage tower sections of the multi-stage polycondensation tower to decrease step by step from 50 KPaA to 10 KPaA from the feed end to the discharge end; (5) Control the operating temperature of the esterification reactor to 220°C~230°C (6) Controlling the operating temperature of the multi-stage tower sections of the multi-stage polycondensation tower to be 225° C. to 235° C.

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