Continuous production plant for low molecular weight polyesters and method for producing the same

Abstract

This invention discloses a continuous production equipment and method for low molecular weight polyester. The production equipment includes a slurry tank, an esterification reactor, a multi-stage polycondensation tower, and an esterification separation tower connected in sequence. The esterification separation tower is also circulatedly connected to the esterification reactor. The slurry tank is used to supply alcohol and acid feedstocks. The esterification reactor is used for the esterification reaction. The multi-stage polycondensation tower includes multiple stages, with the pressure in each stage decreasing progressively from the feed end to the discharge end. The multi-stage polycondensation tower is used to perform polycondensation on the esterified material from the esterification reactor. The polycondensation product generated by the multi-stage polycondensation tower is discharged externally. The esterification separation tower separates water, alcohol, and small molecule substances from the polycondensation condensate. The alcohol separated by the esterification separation tower is refluxed back to the esterification reactor. This application can be used for continuous production of low molecular weight polyester, which can improve efficiency and output while reducing equipment investment and separation energy consumption, thereby reducing energy consumption and costs.

Description

Technical Field

[0001] This application relates to the field of chemical engineering technology, and in particular to a continuous production equipment and method for low molecular weight polyester. Background Technology

[0002] Polyester is a polymer material widely used in textiles, plastics products, and other industrial fields. Polyester production can be divided into two types: batch production and continuous production. Based on molecular weight, polyester includes at least low-molecular-weight polyesters and high-molecular-weight polyesters. Most polyester production volumes are relatively small, therefore, the same production equipment often needs to be switched during production. This results in some low-molecular-weight polyester production being intermittent, which increases production time costs and reduces production efficiency. Summary of the Invention

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

[0004] One embodiment of this application provides a continuous production apparatus for low molecular weight polyester.

[0005] A continuous production line for low molecular weight polyester includes a slurry tank, an esterification reactor, a multi-stage polycondensation tower, and an esterification separation tower connected in sequence. The esterification separation tower is also cyclically connected to the esterification reactor to allow the alcohol separated by the esterification separation tower to be refluxed back to the esterification reactor. The slurry tank is used to supply alcohol and acid feedstocks. The esterification reactor is used to carry out the esterification reaction. The multi-stage polycondensation tower includes multiple tower sections, with the pressure of each tower section decreasing progressively from the feed end to the discharge end. The multi-stage polycondensation tower is used to carry out the polycondensation reaction of the esterified material from the esterification reactor and discharge the resulting polycondensation product. The esterification separation tower is used to separate water, alcohol, and small molecule substances from the polycondensation condensate after vapor-phase condensation from the multi-stage polycondensation tower.

[0006] In some embodiments, the low molecular weight polyester continuous production equipment also satisfies 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 installed on the alcohol raw material pipeline;

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

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

[0010] (1) The low molecular weight polyester continuous production equipment further includes a slurry pump and / or a material control valve, wherein the slurry pump and the material control valve are installed 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 installed 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. A first delivery pump is installed on the first heat exchange pipeline to realize the heat exchange between the polycondensation product generated 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 satisfies at least one of the following conditions:

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

[0014] (2) The esterification reactor includes a multi-stage reaction chamber, and adjacent reaction chambers are separated by a partition with an overflow hole;

[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 installed on the second heat exchange pipe.

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

[0017] In some embodiments, the low molecular weight polyester continuous production equipment also satisfies 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 from top to bottom.

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

[0020] In some embodiments, the low molecular weight polyester continuous production equipment further includes multiple stages of sequentially connected condensers, which are connected to a 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 satisfies at least one of the following conditions:

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

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

[0024] (3) At least one of the condensers is connected to a vacuum unit for partial gas phase reflux and exhaust on the second circulation pipe, and the vacuum unit is connected to the exhaust gas pipe;

[0025] (4) At least one of the condensers is connected to a nitrogen pipeline for replenishing nitrogen, and the nitrogen pipeline is used to realize nitrogen stripping of the multi-stage condensation tower;

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

[0027] (6) A condensation condensate pump is installed on the condensation condensate conveying pipeline.

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

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

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

[0031] One embodiment of this application also provides a method for continuous production of low molecular weight polyester.

[0032] A continuous production method for low molecular weight polyester, using the aforementioned continuous production equipment for low molecular weight polyester, includes the following steps:

[0033] The alcohol and acid are added to the slurry tank, mixed, and then transported to the esterification reactor;

[0034] The esterification reactor is controlled to carry out an esterification reaction to generate esterified materials;

[0035] The esterification material and catalyst are controlled to enter the multi-stage polycondensation tower;

[0036] The multi-stage polycondensation tower is controlled to perform a polycondensation reaction on the esterified material from the esterification reactor. The polycondensation product generated by the multi-stage polycondensation tower is discharged externally. The vapor stripped from the multi-stage polycondensation tower is condensed to form a polycondensation condensate, which then enters the esterification separation tower.

[0037] The esterification separation tower is controlled to separate water, alcohol and small molecule substances in the condensation condensate, and the alcohol separated by the esterification separation tower is returned to the esterification reactor for re-esterification cycle.

[0038] In some embodiments, the continuous production method for low molecular weight polyester also 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℃~100℃;

[0041] (3) Control the residence time of the reactants in each stage of the esterification reactor to be equal;

[0042] (4) The pressure of the multi-stage polycondensation tower is controlled to decrease from 50 kPaA to 10 kPaA in stages from the feed end to the discharge end;

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

[0044] (6) The operating temperature of the multi-stage section of the multi-stage polycondensation tower is controlled to be 225℃~235℃.

[0045] The aforementioned continuous production equipment for low molecular weight polyester can be used for continuous production of low molecular weight polyester. It can improve efficiency and output while reducing equipment investment and separation energy consumption, thereby reducing energy consumption and costs. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings. In the following description, the same reference numerals denote the same parts.

[0048] Figure 1 This is a schematic diagram of a continuous low molecular weight polyester production equipment according to an embodiment of the present invention.

[0049] Explanation of reference numerals in the attached figures

[0050] 10. Continuous production equipment for low molecular weight polyester; 100. Slurry tank; 200. Esterification reactor; 300. Multi-stage polycondensation tower; 400. Esterification separation tower; 500. Acid feed silo; 600. Slurry pump; 700. Material control valve; 800. Cross heat exchanger; 900. External circulation heat exchanger; 1010. First transfer pump; 1020. Second transfer pump; 1100. Esterification material transfer pump; 1110. First-stage condenser; 1120. Second-stage 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 feedstock 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. Exhaust gas pipeline; 1011. Wastewater pipeline. Detailed Implementation

[0051] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0052] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0053] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0054] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0055] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0056] In this document, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain."

[0057] In this application, when numerical intervals (i.e., numerical ranges) are mentioned, unless otherwise specified, the distribution of selectable numerical values ​​within the numerical interval is considered continuous, and includes the two endpoints of the numerical interval (i.e., the minimum and maximum values), as well as every numerical value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that numerical interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, etc.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0059] This application provides a continuous low molecular weight polyester production equipment 10 to solve the problem that some low molecular weight polyester production in the prior art is intermittent, which increases production time costs and reduces production efficiency. The continuous low molecular weight polyester production equipment 10 will be described below with reference to the accompanying drawings.

[0060] The low molecular weight polyester continuous production equipment 10 provided in this application embodiment is exemplary; please refer to [link to example]. Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of the low molecular weight polyester continuous production equipment 10 provided in this application embodiment. The low molecular weight polyester continuous production equipment 10 of this application can be used for continuous production of low molecular weight polyester.

[0061] To more clearly illustrate the structure of the low molecular weight polyester continuous production equipment 10, the following will describe the low molecular weight polyester continuous production equipment 10 in conjunction with the accompanying drawings.

[0062] For example, please refer to Figure 1As shown, a continuous low molecular weight polyester production line 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 cyclically connected to the esterification reactor 200 so that the alcohol separated in the esterification separation tower 400 is refluxed back to the esterification reactor 200. The slurry tank 100 is used to supply alcohol and acid feed. The esterification reactor 200 is used to carry out the esterification reaction. The multi-stage polycondensation tower 300 includes multiple stages. The pressure in each stage decreases progressively from the feed end to the discharge end. The multi-stage polycondensation tower 300 is used to carry out the polycondensation reaction of the esterified material from the esterification reactor 200. The polycondensation product produced by the multi-stage polycondensation tower 300 is discharged externally. The esterification separation tower 400 is used to separate water, alcohol, and small molecule 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 water and small molecules produced by esterification and polycondensation, thereby breaking the reaction equilibrium in the esterification reactor 200 and the multi-stage polycondensation tower 300 and promoting the forward reaction.

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

[0064] The aforementioned low molecular weight polyester continuous production equipment 10 can realize the continuous production of low molecular weight polyester. Compared with traditional batch production, continuous production has many advantages: (1) Improved efficiency and output: In continuous production, reactors, separators and other equipment are connected in series to form a production line. The material flows 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 production efficiency, and realize large-scale batch production. (2) Reduced energy consumption and cost: Continuous production can better utilize thermal energy and other energy sources by optimizing process flow design and operating parameters, thereby significantly reducing the energy consumption per unit of product while producing the same number of products. In addition, the production cost is also reduced due to the reduction of equipment and labor input. (3) Improved uniformity and stability of product quality: In continuous production, the material goes 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 batch production, the product quality of continuous production 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 yield and quality. In summary, continuous production 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 feedstock pipeline 101, and a flow meter is installed on the alcohol feedstock pipeline 101. Preferably, a pump and valve may also be installed on the alcohol feedstock pipeline 101.

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

[0067] In some of these embodiments, please refer to Figure 1 As shown, the low molecular weight polyester continuous production equipment 10 also includes a slurry pump 600 and / or a material control valve 700, the slurry pump 600 and the material control valve 700 being disposed 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 a first heat exchange pipeline 1051, so as to realize the 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 these embodiments, please refer to Figure 1 As shown, a first delivery pump 1010 is installed on the first heat exchange pipe 1051.

[0070] In some embodiments, the esterification reactor 200 is a horizontal reactor. It should be noted that, see [link to relevant documentation] Figure 1 As shown in this 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 multiple reaction chambers. Adjacent reaction chambers are separated by baffles with overflow holes. The size and number of overflow holes on the baffles can be set according to actual needs.

[0072] Preferably, in some embodiments, the esterification reactor 200 includes 3 to 5 stages of 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 transfer pump 1020. The second heat exchange pipe 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 transfer pump 1020 are respectively disposed on the second heat exchange pipe 1052.

[0074] In some of these embodiments, please refer to Figure 1 As shown, the low molecular weight polyester continuous production equipment 10 also includes an esterification material conveying pump 1100. The esterification material conveying pump 1100 is installed on the esterification material conveying pipeline 103 between the esterification reactor 200 and the multi-stage polycondensation tower 300, and the esterification material conveying pipeline 103 is also connected to the catalyst pipeline 104.

[0075] In some embodiments, the multi-stage tower sections of the multi-stage polycondensation tower 300 are distributed vertically, with the feed end of the multi-stage polycondensation tower 300 located at the top and the discharge end located at the bottom, and the pressure of the multi-stage tower sections decreasing gradually from top to bottom.

[0076] In some of these embodiments, please refer to Figure 1 As shown, the multi-stage sections of the multi-stage polycondensation tower 300 are connected in parallel to the polycondensation condensate conveying pipeline 106. Each stage of the tower section is equipped with a valve assembly 1700 on the pipeline connecting to the polycondensation condensate conveying pipeline 106.

[0077] In some embodiments, the operating pressure of the multi-stage sections of the multi-stage polycondensation tower 300 is 5 kPaA to 80 kPaA. In one specific example, the operating pressure of the multi-stage sections is not the same.

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

[0079] Preferably, there can be multiple condensers, which respectively form a primary condenser 1110, a secondary condenser 1120, etc. Please refer to [link / reference]. Figure 1 As shown, Figure 1 A two-stage condenser is shown.

[0080] In some embodiments, the outlet of the subsequent condenser is connected to the preceding condenser via a first circulation pipe 1071 to achieve preheating of the circulating gas.

[0081] In some embodiments, the first-stage condenser is also connected to the multi-stage condensation tower 300 via a second circulation pipe 1072 to achieve partial gas phase reflux to the multi-stage condensation tower 300.

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

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

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

[0085] In some of these embodiments, please refer to Figure 1 As shown, a polycondensate pump 1400 is installed on the polycondensate conveying pipeline 106.

[0086] In some embodiments, the outlet of the esterification reactor 200 is also connected to the esterification separation tower 400. This allows water, alcohol, small molecules, and tetrahydrofuran to enter the esterification separation tower 400 through its outlet for separation.

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

[0088] In some 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 installed 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 gas duct 109. The valve assembly 1700 can be configured 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 automated control.

[0091] One embodiment of this application also provides a method for continuous production of low molecular weight polyester.

[0092] It should be noted that, unless otherwise stated, the reaction steps may be performed in the order described herein or not. For example, other steps may be included between reaction steps, and the order of reaction steps may be appropriately interchanged. This is something that those skilled in the art can determine based on conventional knowledge and experience. Preferably, the reaction methods described herein are performed sequentially.

[0093] A continuous production method for low molecular weight polyester, using the aforementioned continuous production equipment 10 for low molecular weight polyester, includes the following steps:

[0094] Please see Figure 1 As shown, alcohol and acid are added to slurry tank 100, mixed, and then transported to esterification reactor 200.

[0095] The esterification reactor 200 is controlled to carry out the esterification reaction to generate esterified materials.

[0096] Control the esterification materials and catalysts as they enter the multi-stage polycondensation tower 300.

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

[0098] The esterification separation tower 400 is used to separate water, alcohol and small molecules in the polycondensation condensate. The alcohol separated by the esterification separation tower 400 is returned to the esterification reactor 200 for re-esterification and recycling.

[0099] In some embodiments, the above method further includes the following steps: water, alcohol, small molecule substances, and tetrahydrofuran enter the esterification separation tower 400 to achieve separation 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 may be 1, or, for example, 1.5. It is easy to understand that in other examples, the molar ratio of alcohol to acid may also be other values.

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

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

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

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

[0105] In some embodiments, the operating temperature of the multi-stage 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 catalyst functions to accelerate the polycondensation reaction and improve reaction efficiency.

[0107] It should be noted that low molecular weight polyester refers to polyester materials with relatively low molecular weight, whose number average molecular weight (Mn) is usually less than 10,000. Due to their 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, making them easy to recycle. (3) chemical modification: Chemical modification can improve or endow low molecular weight polyesters with 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 an adhesive, coating material, plasticizer, etc. PET has good transparency and mechanical properties, but its melting point and glass transition temperature decrease when the molecular weight is low. (2) Polybutylene succinate (PBS): used to produce biodegradable plastic bags, tableware and other environmentally friendly products. PBS has good biodegradability and can decompose in the natural environment, making it environmentally friendly. (3) Polybutylene adipate (PBA): used as a biomedical material, such as a drug sustained-release carrier, tissue engineering scaffold, etc. PBS has good biocompatibility and biodegradability. (4) Polybutylene octanoate (PBSub): suitable for applications requiring high thermal stability, such as adhesives and coatings at high temperatures. PBS has good crystallinity and heat resistance. (5) Low molecular weight form of polylactic acid (PLA): used in biomedical materials, food packaging, agricultural mulch films, 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 performance can be further optimized through chemical modification.

[0109] In some embodiments, the acids in this application include dibasic acids. For example, the acids in this application include one or more of terephthalic acid (TPA), adipic acid, succinic acid, sebacic acid, and isophthalic acid. Among these, terephthalic acid (TPA) is widely used in the preparation of polyethylene terephthalate (PET). Adipic acid is used in the preparation of nylon 66 and low molecular weight polyesters. Succinic acid is used in the preparation of polybutylene succinate (PBS). Sebacic acid is used in the preparation of biodegradable polyesters. Isophthalic acid is used in the preparation of polyesters with special properties, such as improved heat resistance and chemical stability.

[0110] In some embodiments, the alcohols in this application include diols. For example, the alcohols in this application include one or more of ethylene glycol, butanediol, propylene glycol, neopentyl glycol, and diethylene glycol. Ethylene glycol is widely used in the preparation of PET. Butanediol is used in the preparation of PBS and other low molecular weight polyesters. Propylene glycol is used in the preparation of polyesters with special properties, such as improved biocompatibility. Neopentyl glycol is used in the preparation of polyesters with high heat resistance and chemical resistance. Diethylene glycol is used in the preparation of polyesters with specific properties, such as improved flexibility.

[0111] The continuous production method for low molecular weight polyester in this application includes stages such as batching, separation, esterification, and polycondensation. Specifically, during the batching process, alcohol and acid enter the slurry tank 100 in a certain proportion for continuous pulping, with the temperature generally between 50℃ and 100℃. 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 multi-stage reactions, the closer the esterification reactor 200 and the multi-stage polycondensation tower 300 are to plug flow, the shorter the required residence time. Based on this, in this application, the esterification stage adopts a horizontal multi-chamber esterification reactor 200, with the number of reaction chambers generally being 3 to 5. Esterification separation tower 400 separates water, alcohol, and small molecules, yielding a higher concentration of alcohol. This higher concentration alcohol is then refluxed into the first-stage reaction chamber of esterification reactor 200. This facilitates alcohol recycling, and the recycled alcohol increases the alcohol-acid ratio within esterification reactor 200, thus promoting the esterification reaction rate. The esterified material from esterification reactor 200, mixed with catalyst, is pumped into multi-stage polycondensation tower 300 via esterified material transfer pump 1100. Each section of multi-stage polycondensation tower 300 operates at a different pressure. This design prevents a large amount of alcohol from being instantly removed from the liquid phase when it enters the multi-stage polycondensation tower 300, thus avoiding impact on the molecular weight and molecular weight distribution of the product.

[0112] Example 1

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

[0114] Please see Figure 1 As shown, the low molecular weight polyester continuous production equipment 10 of this embodiment includes a slurry tank 100, an esterification reactor 200, a multi-stage polycondensation 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 transfer pump 1010, a second transfer pump 1020, an esterification material transfer pump 1100, a first-stage condenser 1110, a second-stage condenser 1120, an esterification tower top condenser 1500, and an esterification condensate tank 1600, which are connected in sequence.

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

[0116] The esterification reactor 200 is a horizontal reactor. It includes three reaction chambers, with adjacent chambers separated by baffles having overflow holes. An esterification separation tower 400 is also connected to the esterification reactor 200 in a circulating manner. A second heat exchange pipe 1052 is located outside the esterification reactor 200 and connects to its circulation outlet and inlet. An external circulation heat exchanger 900 and a second transfer pump 1020 are respectively installed on the second heat exchange pipe 1052. An esterification material transfer pump 1100 is installed on the esterification material transfer pipe 103 between the esterification reactor 200 and the multi-stage polycondensation tower 300. The esterification material transfer pipe 103 is also connected to a 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 comprises four tower sections. The multi-stage tower sections of the multi-stage polycondensation tower 300 are distributed vertically, with the feed end of the multi-stage polycondensation tower 300 located at the top and the discharge end 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. A first delivery pump 1010 is installed on the first heat exchange pipe 1051.

[0119] The primary condenser 1110 and the secondary condenser 1120 are sequentially connected to the polycondensation condensate conveying pipeline 106 between the multi-stage polycondensation tower 300 and the esterification separation tower 400. The outlet of the secondary condenser 1120 is connected to the primary condenser 1110 via a first circulation pipeline 1071 to preheat the circulating gas. The primary condenser 1110 exchanges heat between the return gas and the gas phase to be condensed, achieving energy saving. A vacuum unit 1200 for partial gas phase reflux and exhaust is connected to the first circulation pipeline 1071 of the secondary condenser 1120, and the vacuum unit 1200 is connected to the waste gas pipeline 109. A nitrogen pipeline 108 for replenishing nitrogen is also connected to the first circulation pipeline 1071 of the secondary condenser 1120. The primary condenser 1110 is also connected to the multi-stage polycondensation tower 300 via a second circulation pipeline 1072 to achieve partial gas phase reflux to the multi-stage polycondensation tower 300. A condensate tank 1300 is connected to the condensate delivery pipeline 106 at the location of the secondary condenser 1120. A condensate pump 1400 is installed on the condensate delivery pipeline 106.

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

[0121] Example 2

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

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

[0124] 1,4-Butanediol and adipic acid in a molar ratio of 1.3 are added to slurry tank 100 and mixed. The operating temperature of slurry tank 100 is 60°C. The mixture is then conveyed to esterification reactor 200.

[0125] The residence time of the mixture in the three-stage reaction chamber of the esterification reactor 200 is 3 hours. The operating temperature of the esterification reactor 200 is 220℃. The esterification reactor 200 is controlled to carry out the esterification reaction to generate esterified materials.

[0126] The esterification material and catalyst are controlled to enter the multi-stage polycondensation tower 300. The pressures of the four stages of the multi-stage polycondensation tower 300 are controlled to be 50 kPaA, 40 kPaA, 30 kPaA, and 10 kPaA respectively from the feed end to the discharge end. The residence times of the esterification material in the four stages are 3 h, 3 h, 2 h, and 1 h respectively. The operating temperature of the multi-stage sections of the multi-stage polycondensation tower 300 is controlled to be 225 °C. The multi-stage polycondensation tower 300 controls the polycondensation reaction of the esterification material from the esterification reactor 200. The polycondensation product produced by the multi-stage polycondensation tower 300 is discharged after heat exchange in the cross heat exchanger 800. The vapor phase stripped from the multi-stage polycondensation tower 300 is condensed to form a polycondensation condensate which enters the esterification separation tower 400.

[0127] The esterification separation tower 400 is used to separate water, alcohol and small molecules in the polycondensation condensate. The alcohol separated by the esterification separation tower 400 is returned to the esterification reactor 200 for re-esterification and recycling.

[0128] The final esterified material has a hydroxyl value of 105 and an acid value of 15, while the polycondensation product has a hydroxyl value of 56, an acid value of 0.16, and a molecular weight of 2000.

[0129] Example 3

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

[0131] The continuous low molecular weight polyester production method of this embodiment uses the same continuous low molecular weight polyester production equipment 10 as in Example 1. The difference is that, in this embodiment, the esterification reactor 200 of the continuous low molecular weight polyester production equipment 10 includes four-stage reaction chambers, and the multi-stage polycondensation tower 300 includes five-stage tower sections, including the following steps:

[0132] 1,6-hexanediol and adipic acid in a molar ratio of 1.06 are added to slurry tank 100 and mixed. The operating temperature of slurry tank 100 is 60°C. The mixture is then conveyed to esterification reactor 200.

[0133] The residence times of the mixture in the four-stage reaction chambers of the esterification reactor 200 are 5h, 3h, 3h, and 3h, respectively. The operating temperature of the esterification reactor 200 is 230℃, and the esterification reactor 200 is controlled to carry out the esterification reaction to generate esterified materials.

[0134] The esterification material and catalyst are controlled to enter the multi-stage polycondensation tower 300. The pressures of the five stages of the multi-stage polycondensation tower 300 are controlled sequentially from the feed end to the discharge end as 50 kPaA, 30 kPaA, 20 kPaA, 15 kPaA, and 10 kPaA. The residence times of the esterification material in the five stages are 5 h, 3 h, 3 h, 2 h, and 1 h, respectively. The operating temperature of the multi-stage sections of the multi-stage polycondensation tower 300 is controlled at 235 °C. The multi-stage polycondensation tower 300 controls the polycondensation reaction of the esterification material from the esterification reactor 200. The polycondensation product produced by the multi-stage polycondensation tower 300 is discharged after heat exchange in the cross heat exchanger 800. The vapor phase stripped from the multi-stage polycondensation tower 300 is condensed to form a polycondensation condensate, which enters the esterification separation tower 400.

[0135] The esterification separation tower 400 is used to separate water, alcohol and small molecules in the polycondensation condensate. The alcohol separated by the esterification separation tower 400 is returned to the esterification reactor 200 for re-esterification and recycling.

[0136] The final esterified material has a hydroxyl value of 38 and an acid value of 8, while the polycondensation product has a hydroxyl value of 28.6, an acid value of 0.18, and a molecular weight of 4000.

[0137] Based on Examples 1 and 2, it can be seen that the low molecular weight polyester continuous production equipment 10 of this 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) Based on 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, promote the forward reaction, shorten the residence time required for the reaction and reduce equipment investment.

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

[0141] (3) The multi-stage polycondensation tower 300 adopts different operating pressures for each stage of the tower, and the pressure of the tower section decreases step by step to achieve controllable molecular weight of the produced product.

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

[0143] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0144] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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 embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A continuous production equipment for low molecular weight polyester, characterized in that, The system includes a slurry tank, an esterification reactor, a multi-stage polycondensation tower, an esterification separation tower, and a cross heat exchanger, connected in sequence. The esterification separation tower is also cyclically connected to the esterification reactor to allow the alcohol separated by the esterification separation tower to be refluxed back to the esterification reactor. The slurry tank is used to supply alcohol and acid feeds. The esterification reactor is used to carry out the esterification reaction. The multi-stage polycondensation tower includes multiple tower sections, with the pressure of each section decreasing progressively from the feed end to the discharge end. The multiple tower sections of the multi-stage polycondensation tower are distributed along a vertical direction. The feed end of the polycondensation tower is located at the top and the discharge end is located at the bottom. The pressure of the multi-stage tower sections decreases gradually from top to bottom. The multi-stage polycondensation tower is used to carry out polycondensation reaction on the esterified material from the esterification reactor and discharge the resulting polycondensation product. The esterification separation tower is used to separate small molecules in the polycondensation condensate after the gas phase condensation from the multi-stage polycondensation tower. The cross heat exchanger is installed 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.

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 installed on the alcohol raw material pipeline; (2) The slurry tank is connected to an acid feed hopper.

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 includes a slurry pump and / or a material control valve, wherein the slurry pump and the material control valve are installed on the slurry pipeline between the slurry tank and the esterification reactor; (2) A first delivery pump is provided on the first heat exchange pipeline to realize the heat exchange between the polycondensation product generated by the multi-stage polycondensation tower and the slurry in the slurry pipeline by the cross heat exchanger.

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 includes a multi-stage reaction chamber, and adjacent reaction chambers are separated by a partition with an overflow hole; (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 installed 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 also includes an esterification material conveying pump, which is installed on the esterification material conveying pipeline between the esterification reactor and the multi-stage polycondensation tower, and the esterification material conveying pipeline is also connected to a catalyst pipeline. (2) The operating pressure of the multi-stage 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, with the multi-stage condenser 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 outlet of the condenser in the next stage is connected to the condenser in the previous stage through the first circulation pipe to achieve preheating of the circulating gas; (2) The first-stage condenser is also connected to the multi-stage polycondensation tower through a second circulation pipe to achieve partial gas phase reflux to the multi-stage polycondensation tower; (3) At least one of the first circulation pipes of the condenser is connected to a vacuum unit for realizing partial gas phase reflux and exhaust, and the vacuum unit is connected to the exhaust gas pipe; (4) At least one of the first circulation pipes of the condenser is connected to a nitrogen pipe for replenishing nitrogen, and the nitrogen pipe is used to realize nitrogen stripping of the multi-stage condensation tower; (5) A condensate tank is connected to the condensate conveying pipeline at the position of the last stage of the condenser; (6) A condensation condensate pump is installed on the condensation condensate conveying 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 outlet of the esterification reactor is also connected to the esterification separation tower; (2) The outlet of the esterification separation tower is sequentially connected to the top condenser of the esterification tower and the esterification condensate tank. The outlet of the top condenser of the esterification tower is connected to the waste gas pipeline, and the outlet of the top condenser of the esterification tower is connected to the esterification condensate tank. The esterification condensate tank is also connected to the wastewater pipeline and the esterification separation tower to realize the discharge and re-separation of the esterification condensate, respectively.

9. A continuous production method for low molecular weight polyester, characterized in that, The continuous production equipment for low molecular weight polyester according to any one of claims 1 to 8 includes the following steps: The alcohol and acid are added to the slurry tank, mixed, and then transported to the esterification reactor; The esterification reactor is controlled to carry out an esterification reaction to generate esterified materials; The esterification material and catalyst are controlled to enter the multi-stage polycondensation tower; The multi-stage polycondensation tower is controlled to carry out polycondensation reaction on the esterification material from the esterification reactor. The polycondensation product generated by the multi-stage polycondensation tower is discharged externally. The gas phase stripped by the multi-stage polycondensation tower is condensed and forms a polycondensation condensate that enters the esterification separation tower. as well as The esterification separation tower is controlled to separate small molecules in the polycondensation condensate, and the alcohol separated by the esterification separation tower is refluxed to the esterification reactor for re-esterification cycle.

10. The continuous production method for low molecular weight polyester according to claim 9, characterized in that, The continuous production method for low molecular weight polyester also satisfies 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℃~100℃; (3) Control the residence time of the reactants in each stage of the esterification reactor to be equal; (4) The pressure of the multi-stage polycondensation tower is controlled to decrease from 50 kPaA to 10 kPaA in stages from the feed end to the discharge end; (5) The operating temperature of the esterification reactor is controlled to be 220℃~230℃; (6) The operating temperature of the multi-stage section of the multi-stage polycondensation tower is controlled to be 225℃~235℃.

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