System and method for preparing polyester polyol prepolymer

Abstract

The invention provides a system and a method for preparing a polyester polyol prepolymer. The system comprises a normal-pressure bubbling reaction rectifying tower and a reduced-pressure heating reaction rectifying tower. The method comprises the following steps: enabling protective gas to enter a normal-pressure bubbling reaction rectifying tower, and enabling raw materials for preparing a polyester polyol prepolymer to enter the normal-pressure bubbling reaction rectifying tower for primary esterification or ester exchange reaction; and enabling the primary esterification or ester exchange product to enter a reduced-pressure heating reactive distillation tower, and carrying out one or more of deep esterification reaction, ester exchange reaction and pre-polycondensation reaction to obtain the polyester polyol prepolymer. The system and the method provided by the invention are a system and a method for continuously preparing the polyester polyol prepolymer, which are high in integration level, convenient to operate and free of mechanical stirring. The method has the advantages of high reaction efficiency, stable product quality, easiness in product separation, convenience in large-scale production and the like.

Description

Technical Field

[0001] The invention relates to a system and a method for preparing a polyester polyol prepolymer, and belongs to the technical field of preparation of polyester polyols. Background Art

[0002] Polyester polyols are usually linear polymers made from organic dicarboxylic acids (or anhydrides, esters) and diols (or polyols) through esterification (or transesterification), polycondensation and other reactions. Polyester polyols are one of the main raw materials for materials such as biodegradable plastics and engineering plastics. They are widely used in food packaging, fibers, films and other fields, and have broad market prospects. The preparation of polyester polyols is usually divided into two stages: esterification and polycondensation. In the esterification stage, the acid and alcohol react to generate a large amount of water. The water is separated from the small amount of alcohol entrained by the distillation column and then removed from the system, driving the reaction in the direction of esterification.

[0003] At present, the traditional polyester polyol production process is mostly an intermittent process. Although the intermittent production method is flexible and can easily switch between multiple brands, its product quality fluctuates greatly, and the mass transfer and heat transfer process is limited, the device utilization rate is low, and the energy loss caused by repeated temperature increases and decreases is large. In addition, the esterification reaction for preparing polyester polyols is a reversible process. In order to promote the reaction in the direction of esterification, it is key to quickly and efficiently remove the generated byproduct small molecule water. Traditional reactors accelerate the removal of small molecules by strengthening stirring or bubbling with nitrogen, but these methods have high energy consumption and limited effects.

[0004] US5786443A discloses a method for preparing polyester prepolymer. In this method, after esterifying dibasic acid and diol, the product is allowed to flow downward into a countercurrent tower reactor, and the protective gas rises through the tower reactor, and the obtained product has a low content of terminal carboxyl groups. However, the shortcomings of this preparation method include: the precondensation reactor has low operating flexibility, short residence time and many dead zones, and self-cleaning requires vigorous bubbling; in addition, this method does not optimize the esterification process.

[0005] CN1137278A discloses a continuous polyester production method. In this method, terephthalic acid TPA (or dimethyl terephthalate DMT) and ethylene glycol are continuously esterified (or transesterified) in an esterification tower, and then enter a prepolymerization tower for polycondensation. A protective gas is introduced into the reactor in the opposite direction to the polymer to remove volatile by-products. The shortcomings of this method include: the esterification stage is not optimized, and the pre-polycondensation reactor has low operating flexibility and needs to rely on violent bubbling to achieve self-cleaning; in addition, the reaction unit and the separation unit are independent and not integrated.

[0006] CN102432846A discloses a method and device for continuously producing polyester polyols. The method and device adopt a two-stage reaction device, the process residence time is uniform and controllable, and the heat transfer and mass transfer process are strengthened. However, the reaction process and separation process of the process are still carried out in two independent units, and the multi-stage separation effect of the tower reactor is not fully utilized.

[0007] CN102585191A discloses a tower reactor and its application for continuous production of polyester polyols. This patent application designs a multi-stage bubbling tower reactor with higher integration, and prepares polyester polyols by esterification (or transesterification) reaction and polycondensation reaction of polycarboxylic acid (or polycarboxylic acid derivative) and polyol (or polyol derivative). The reaction raw materials move from top to bottom and overflow on the tower plate, and the protective gas, small molecule steam generated by the reaction and vaporized polyol are discharged from the system from bottom to top through the bubbling air pipe. A packing tower section is added to the top of the reactor, which can separate the top steam and reflux most of the alcohol. The reactor has the advantages of high degree of automation and short reaction time. However, the shortcomings of this technology include: there is a certain dead zone in the reactor and the bubbling air pipe is not easy to clean, and it is necessary to rely on violent bubbling to achieve mass transfer enhancement and self-cleaning; there are high requirements for the control of the temperature of each section of the reactor; during operation, vacuum and nitrogen supplementation are operated in the same reactor, and the requirements for stable control are high; when used in the esterification stage, the vacuum may extract the oligomers, affecting the yield and the stability of the vacuum system.

[0008] In the preparation process of polyester polyols, in the early stage of esterification (or transesterification) reaction, the main materials in the reactor include a large amount of raw small molecule alcohols. The small molecule alcohols and the water generated by the reaction make the boiling point of the initial reaction liquid relatively low. Therefore, if the reaction temperature is increased, there will be a safety hazard of boiling, and it may also cause excess alcohol to be extracted from the top of the reactor along with water, resulting in an imbalance in the raw material ratio, fluctuations in product indicators and waste of raw materials. Gradually increasing the temperature is conducive to precise control according to the reaction process.

[0009] Therefore, developing a new system and method for preparing polyester polyol prepolymers has become one of the urgent problems to be solved in this field. Summary of the invention

[0010] In order to solve the above technical problems, the purpose of the present invention is to provide a system and method for preparing polyester polyol prepolymer. The present invention has the advantages of high integration, can integrate reaction and separation in the same device, and has high reaction efficiency.

[0011] In order to achieve the above-mentioned object, the first aspect of the present invention provides a system for preparing polyester polyol prepolymer, the system comprising: a normal pressure bubbling reaction distillation tower and a reduced pressure temperature reaction distillation tower;

[0012] The tower body of the atmospheric bubbling reaction distillation tower includes a first separation section and a first reaction section from top to bottom, the first separation section is provided with a first separation packing layer, and the first reaction section is provided with a plurality of tower trays;

[0013] The atmospheric bubbling reaction distillation tower is provided with a first gas phase discharge port, a first liquid phase discharge port, a first raw material inlet and a protective gas inlet;

[0014] The tower body of the vacuum temperature-raising reaction distillation tower includes a second separation section and a second reaction section from top to bottom, the second separation section is provided with a second separation packing layer, and the second reaction section is provided with a plurality of tower trays;

[0015] The vacuum temperature reaction distillation tower is provided with a second gas phase discharge port, a second liquid phase discharge port and a second raw material inlet;

[0016] The first liquid phase discharge port of the atmospheric pressure bubbling reaction distillation tower is connected to the second raw material inlet of the vacuum temperature rising reaction distillation tower through a pipeline.

[0017] In the present invention, it should be noted that the polyester polyol prepolymer described in the present invention is an intermediate product in the process of preparing polyester polyol, and the prepolymer can be further polycondensed to obtain polyester polyol.

[0018] In the above-mentioned system for preparing polyester polyol prepolymer, the atmospheric bubbling reaction distillation tower is used to carry out preliminary esterification or transesterification reaction of the raw materials, and the reduced pressure temperature reaction distillation tower is used to carry out one or more of deep esterification reaction, transesterification reaction and pre-polycondensation reaction on the preliminary esterification or transesterification product obtained by the atmospheric bubbling reaction distillation tower to obtain polyester polyol prepolymer, which is discharged from the second liquid phase discharge port of the reduced pressure temperature reaction distillation tower.

[0019] According to a specific embodiment of the present invention, the raw materials entering from the first raw material inlet of the atmospheric bubbling reaction distillation tower include a mixed solution of one or more of polycarboxylic acids and their derivatives, polyols and catalysts. Among them, the derivatives of polycarboxylic acids may include anhydrides and / or esters formed by polycarboxylic acids.

[0020] According to a specific embodiment of the present invention, preferably, the system for preparing the polyester polyol prepolymer further comprises: a polyol storage device, and the vacuum temperature reaction distillation tower further comprises a spray device; the spray device is arranged inside the tower body of the vacuum temperature reaction distillation tower, and the spray device is arranged above the second separation packing layer; the spray device is connected to the polyol storage device through a pipeline, and is used to spray polyols into the vacuum temperature reaction distillation tower. More preferably, the spray device at least comprises a spray pipe and a nozzle connected to the spray pipe, and the side wall of the vacuum temperature reaction distillation tower is provided with a polyol feed port, the polyol feed port is located above the second separation packing layer of the vacuum temperature reaction distillation tower, and the spray pipe is connected to the polyol feed port. The present invention preferably arranges a spray device in the vacuum temperature reaction distillation tower to facilitate the reflux of polyols and oligomers in the reaction system, as well as the control of carboxyl content and the adjustment of esterification rate or transesterification rate.

[0021] In the above polyester polyol prepolymer preparation system, preferably, the tower bodies of the atmospheric bubbling reaction distillation tower and the reduced pressure temperature reaction distillation tower are respectively provided with heating jackets, which are used to heat the two reaction distillation towers to the temperature required for the reaction.

[0022] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, several trays in the atmospheric bubbling reaction distillation tower and the reduced pressure temperature reaction distillation tower have a multi-stage overflow structure. More preferably, the trays include one or a combination of inclined hole trays, bubble cap trays, fixed valve trays and vertical sieve plate trays. Further preferably, the trays are inclined hole trays.

[0023] According to a specific embodiment of the present invention, preferably, the system for preparing the polyester polyol prepolymer further comprises: a vacuum device, which is connected to the second gas phase discharge port of the vacuum temperature reaction distillation tower through a pipeline. The vacuum device is used to adjust the pressure in the vacuum temperature reaction distillation tower to the pressure required for the reaction.

[0024] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the filler in the first separation filler layer of the atmospheric pressure bubbling reaction distillation tower is a random filler or a structured filler.

[0025] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the filler in the second separation filler layer of the vacuum temperature reaction distillation tower is a random filler or a structured filler.

[0026] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the top of the atmospheric pressure bubbling reaction distillation tower is provided with the first gas phase discharge port; the bottom of the atmospheric pressure bubbling reaction distillation tower is provided with the first liquid phase discharge port; the side wall of the atmospheric pressure bubbling reaction distillation tower is provided with the first raw material inlet, and the first raw material inlet is located in the first reaction section; the side wall of the atmospheric pressure bubbling reaction distillation tower is provided with the protective gas inlet, and the protective gas inlet is located below the first reaction section.

[0027] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the top of the vacuum temperature reaction distillation tower is provided with the second gas phase discharge port; the bottom of the vacuum temperature reaction distillation tower is provided with the second liquid phase discharge port; the side wall of the vacuum temperature reaction distillation tower is provided with the second raw material inlet, and the second raw material inlet is located in the second reaction section.

[0028] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the protective gas inlet of the atmospheric pressure bubbling reaction distillation tower is a tangential inlet, which is tangential to the side wall of the atmospheric pressure bubbling reaction distillation tower. More preferably, the protective gas inlet of the atmospheric pressure bubbling reaction distillation tower is arranged tangentially and obliquely downward on the side wall of the atmospheric pressure bubbling reaction distillation tower along the air inlet direction, so that the protective gas enters tangentially along the oblique downward direction, and the protective gas inlet is 15 to 85° with the horizontal direction of the cross section of the atmospheric pressure bubbling reaction distillation tower. The protective gas inlet arranged tangentially and obliquely downward on the side wall of the atmospheric pressure bubbling reaction distillation tower can make the protective gas enter the tower body tangentially and obliquely downward along the side wall of the atmospheric pressure bubbling reaction distillation tower for bubbling, which is beneficial to strengthen the mixing of materials, the separation of products and by-products, and avoid the blockage of the protective gas inlet.

[0029] In the above-mentioned system for preparing polyester polyol prepolymer, preferably, the number of the protective gas inlet of the atmospheric pressure bubbling reaction distillation tower is multiple, and each protective gas inlet is a tangential inlet, and the multiple protective gas inlets are evenly arranged along the circumferential direction on the side wall of the atmospheric pressure bubbling reaction distillation tower.

[0030] A second aspect of the present invention provides a method for preparing a polyester polyol prepolymer, wherein the method adopts the above-mentioned system for preparing a polyester polyol prepolymer, and the method comprises the following steps:

[0031] (1) allowing a protective gas to enter an atmospheric pressure bubbling reaction distillation tower, and allowing a raw material for preparing a polyester polyol prepolymer to enter the atmospheric pressure bubbling reaction distillation tower, the raw material for preparing a polyester polyol prepolymer undergoes a preliminary esterification or transesterification reaction, the generated by-products and gaseous substances in the reaction system pass through a first separation filler layer, the by-products and protective gas are discharged from the atmospheric pressure bubbling reaction distillation tower from a first gas phase discharge port, and the generated preliminary esterification or transesterification products are discharged from the atmospheric pressure bubbling reaction distillation tower from a first liquid phase discharge port;

[0032] (2) The preliminary esterification or transesterification product discharged from the first liquid phase discharge port enters a vacuum temperature reaction distillation tower to undergo one or more of a deep esterification reaction, a transesterification reaction, and a pre-polycondensation reaction. After the generated by-products and the gas phase substances in the reaction system pass through a second separation packing layer, the by-products are discharged from the vacuum temperature reaction distillation tower from the second gas phase discharge port, and the generated polyester polyol prepolymer is discharged from the second liquid phase discharge port.

[0033] In step (1) of the above method, the by-products generated mainly include water and / or tetrahydrofuran, etc., and the gaseous substances in the reaction system mainly include the by-products generated, polyols and oligomers generated by the reaction, etc. These gaseous substances pass through the first separation filler layer, so that the polyols and oligomers generated by the reaction can be separated and refluxed in time, while the by-products are discharged from the top of the tower.

[0034] In step (2) of the above method, if a deep esterification reaction and / or an ester exchange reaction is carried out in a vacuum temperature reaction distillation tower, the by-products generated mainly include water and / or tetrahydrofuran, etc., and the gaseous substances in the reaction system mainly include the generated by-products, polyols and oligomers generated by the reaction, etc. These gaseous substances can be separated and refluxed in time from the polyols and oligomers generated by the reaction through the second separation packing layer, and the by-products are discharged from the top of the tower; if a pre-polycondensation reaction is carried out in a vacuum temperature reaction distillation tower, the by-products generated mainly include water and / or tetrahydrofuran, polyols, and the by-products and oligomers generated by the reaction can be separated and refluxed in time from the oligomers generated by the reaction through the second separation packing layer, and the by-products are discharged from the top of the tower.

[0035] In the above method, preferably, in step (1), the raw materials for preparing the polyester polyol prepolymer include a mixture of one or more of polycarboxylic acids and their derivatives, polyols and catalysts. The derivatives of polycarboxylic acids may include anhydrides and / or esters formed by polycarboxylic acids, such as but not limited to terephthalic acid, succinic acid, dimethyl terephthalate, dimethyl succinate, succinic anhydride, etc. Polycarboxylic acids and their derivatives and polyols may all be raw materials for preparing polyester polyols conventionally used in the art, and the present invention does not specifically limit them.

[0036] According to a specific embodiment of the present invention, preferably, the catalyst comprises one or a combination of titanium, tin, antimony, zirconium and bismuth catalysts. More preferably, the catalyst comprises one or a combination of isopropyl titanate, tetrabutyl titanate, titanium composite catalyst, dibutyltin dilaurate, stannous octoate, 1-chloro-3-hydroxy-1,1,3,3-tetrabutoxydistannoxane (CHTD) and bismuth laurate.

[0037] According to a specific embodiment of the present invention, preferably, the molar ratio of the combination of one or more of the polycarboxylic acids and their derivatives to the polyol is 1:4 to 1.5:1.

[0038] According to a specific embodiment of the present invention, preferably, the amount of the catalyst used is 10 to 5000 ppm of the mass of one or a combination of several of the polycarboxylic acids and their derivatives.

[0039] In the above method, preferably, in step (1), the protective gas enters the interior of the tower body downward along the tangential inclination of the side wall of the atmospheric pressure bubbling reaction distillation tower.

[0040] In the above method, preferably, in step (1), the protective gas includes nitrogen or the like.

[0041] In the above method, preferably, in step (1), the raw materials for preparing the polyester polyol prepolymer are continuously fed into a normal pressure bubbling reaction distillation tower.

[0042] In the above method, preferably, in step (1), the temperature of the preliminary esterification or transesterification reaction is 130 to 260°C, more preferably 140 to 200°C.

[0043] In the above method, preferably, the esterification rate or transesterification rate of step (1) is 50-95%, more preferably 60-90%. It should be noted that the esterification rate or transesterification rate is calculated as follows: the molar amount of the polycarboxylic acid or its derivative participating in the reaction / the molar amount of the polycarboxylic acid or its derivative that can react theoretically × 100%.

[0044] In the above method, preferably, step (2) further comprises: using a spray device in the vacuum temperature reaction distillation tower to spray the polyol into the vacuum temperature reaction distillation tower to participate in the reaction and prevent the polyol and oligomer from being entrained out of the system by the gas phase. More preferably, the mass ratio of the polyol sprayed into the vacuum temperature reaction distillation tower by the spray device to the mass ratio of the preliminary esterification or transesterification product is 0.02 to 5, and more preferably 0.2 to 2.

[0045] In the above method, preferably, in step (2), the temperature of one or more of the deep esterification reaction, the transesterification reaction and the pre-polycondensation reaction is 150 to 260°C, more preferably 180 to 240°C.

[0046] In the above method, preferably, in step (2), the pressure of one or more of the deep esterification reaction, the transesterification reaction and the pre-polycondensation reaction is 15 to 101.325 kPa, more preferably 50 to 100 kPa.

[0047] In the above method, preferably, the esterification rate or transesterification rate in step (2) is 90 to 99%, more preferably 95 to 99%.

[0048] The present invention provides a system and method for preparing polyester polyol prepolymers. Based on the staged characteristics of the reaction process in the preparation of polyester polyol prepolymers, the present invention designs a system and method for preparing polyester polyol prepolymers by reactive distillation intensification from the perspectives of accelerating the reaction rate, improving the reaction process, promoting product separation, optimizing energy coupling, etc. The system of the present invention mainly comprises a normal pressure bubbling reaction distillation tower and a reduced pressure temperature reaction distillation tower. A protective gas is bubbled into the normal pressure bubbling reaction distillation tower, and a mixed solution of one or more combinations of polycarboxylic acids and their derivatives, polyols and catalysts are continuously introduced into the normal pressure bubbling reaction distillation tower to carry out a preliminary esterification or transesterification reaction. The generated gas phase byproducts (mainly comprising water and / or tetrahydrofuran, etc.) are purified by a first separation packing layer, evaporated out of the normal pressure bubbling reaction distillation tower and collected from the tower top; the tower bottom discharge of the normal pressure bubbling reaction distillation tower enters a reduced pressure temperature reaction distillation tower to carry out one or more of deep esterification reaction, transesterification reaction and pre-polycondensation reaction. The generated gas phase byproducts are purified by a second separation packing layer, evaporated out of the reduced pressure temperature reaction distillation tower, and a polyester polyol prepolymer is obtained.

[0049] The system and method provided by the present invention have the advantage of integrating reaction and separation in the same device. By carrying out the preparation process in stages and designing corresponding equipment structures and processes, the reaction process can be strengthened and the preparation efficiency of polyester polyol prepolymer can be improved, thereby being applied to the production of polyester polyol.

[0050] The technical solution of the present invention has at least the following beneficial effects:

[0051] 1. Taking full account of the staged characteristics of the polyester polyol prepolymer preparation process, the reaction process is divided into normal pressure bubbling reaction and reduced pressure heating reaction. In the early stage of esterification or transesterification reaction, the viscosity of the reaction system is low, and the normal pressure bubbling method is used to promote the mixing of reactants and the separation of by-products such as water and / or tetrahydrofuran from the esterification or transesterification products, thereby accelerating the progress of the reaction; in the middle and late stages of esterification or transesterification reaction and pre-polycondensation reaction, the reduced pressure heating method is used to promote the forward progress of the reaction.

[0052] 2. In the atmospheric bubbling reaction distillation tower, the protective gas enters the tower body at a tangential angle downward for bubbling, which is beneficial to enhance material mixing, separation of products and by-products, and avoid blockage of the protective gas inlet.

[0053] 3. The advantage of reactive distillation in coupling reaction and distillation is brought into play, and the by-products (water and / or tetrahydrofuran, etc.) produced in the esterification or ester exchange process, or the by-products (water and / or tetrahydrofuran and polyols, etc.) produced in the pre-condensation process are evaporated, which promotes the reaction process and realizes energy integration.

[0054] 4. The upper part of the tower body of the atmospheric bubbling reaction distillation tower is provided with a first separation packing layer, which can separate and reflux the polyols and the oligomers generated by the reaction in time, avoiding the increase of the carboxyl content in the reaction system and the decrease of the yield; the upper part of the tower body of the reduced pressure temperature reaction distillation tower is provided with a second separation packing layer and preferably a spray device, which can not only separate and reflux the polyols and the oligomers generated by the reaction, but also facilitate the control of the carboxyl content in the reaction system and the adjustment of the esterification rate or the ester exchange rate.

[0055] In summary, the system and method provided by the present invention is a system and method for continuously preparing polyester polyol prepolymers with high integration, easy operation and no mechanical stirring. The present invention has the advantages of high reaction efficiency, stable product quality, easy product separation, and convenience for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic diagram of the structure of a system for preparing polyester polyol prepolymer in some specific embodiments of the present invention.

[0057] Figure 2 It is a schematic structural diagram of a system for preparing polyester polyol prepolymer in other specific embodiments of the present invention.

[0058] Description of Figure Numbers:

[0059] 1-normal pressure bubbling reaction distillation tower; 2-reduced pressure temperature reaction distillation tower; 3-polyol storage device; 4-vacuum device; 5-heating jacket;

[0060] 101-first separation section; 102-first reaction section; 103-first separation packing layer; 104-first tray; 105-first gas phase discharge port; 106-first liquid phase discharge port; 107-first raw material inlet; 108-protective gas inlet;

[0061] 201 - second separation section; 202 - second reaction section; 203 - second separation packing layer; 204 - second tower plate; 205 - second gas phase discharge port; 206 - second liquid phase discharge port; 207 - second raw material inlet; 208 - spray device; 209 - spray pipe; 210 - nozzle. DETAILED DESCRIPTION

[0062] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0063] Example 1

[0064] This embodiment provides a system for preparing polyester polyol prepolymers. The structure of the system is as follows: Figure 1 shown.

[0065] The system comprises: a normal pressure bubbling reaction distillation tower 1, a reduced pressure temperature reaction distillation tower 2 and a vacuum device 4.

[0066] The tower body of the atmospheric bubbling reaction distillation tower 1 includes a first separation section 101 and a first reaction section 102 from top to bottom. The first separation section is provided with a first separation packing layer 103 , and the first reaction section is provided with a plurality of first tower plates 104 .

[0067] A first gas phase discharge port 105 is provided at the top of the atmospheric pressure bubbling reaction distillation tower 1, and a first liquid phase discharge port 106 is provided at the bottom of the atmospheric pressure bubbling reaction distillation tower 1; a first raw material inlet 107 is provided at the side wall of the atmospheric pressure bubbling reaction distillation tower, and the first raw material inlet 107 is located in the first reaction section 102; a protective gas inlet 108 is provided at the side wall of the atmospheric pressure bubbling reaction distillation tower, and the protective gas inlet 108 is located below the first reaction section 102.

[0068] The tower body of the vacuum temperature reaction distillation tower 2 includes a second separation section 201 and a second reaction section 202 from top to bottom. The second separation section 201 is provided with a second separation packing layer 203 , and the second reaction section is provided with a plurality of second trays 204 .

[0069] A second gas phase discharge port 205 is provided at the top of the vacuum temperature reaction distillation tower 2, and a second liquid phase discharge port 206 is provided at the bottom of the vacuum temperature reaction distillation tower 2; a second raw material inlet 207 is provided on the side wall of the vacuum temperature reaction distillation tower 2, and the second raw material inlet 207 is located in the second reaction section 202.

[0070] The first liquid phase discharge port 106 of the atmospheric pressure bubbling reaction distillation tower 1 is connected to the second raw material inlet 207 of the vacuum temperature rising reaction distillation tower 2 through a pipeline.

[0071] The tower bodies of the atmospheric bubbling reaction distillation tower 1 and the reduced pressure temperature reaction distillation tower 2 are respectively provided with heating jackets 5 for heating the two reaction distillation towers to the temperature required for the reaction.

[0072] The plurality of first trays 104 in the atmospheric bubbling reaction distillation tower 1 have a multi-stage overflow structure. The plurality of second trays 204 in the vacuum temperature reaction distillation tower 2 also have a multi-stage overflow structure. The first tray 104 and the second tray 204 have the same structure. Specifically, the first tray 104 and the second tray 204 are both inclined hole trays.

[0073] The vacuum device 4 is connected to the second gas phase discharge port 205 of the vacuum temperature-elevating reaction distillation tower 2 through a pipeline, and is used to adjust the pressure of the vacuum temperature-elevating reaction distillation tower 2 to the pressure required for the reaction.

[0074] The packing in the first separation packing layer 103 of the atmospheric bubbling reaction distillation tower 1 includes random stacked saddle ring packing.

[0075] The packing in the second separation packing layer 203 of the vacuum temperature reaction distillation tower 2 includes random stacked rectangular saddle ring packing.

[0076] The protective gas inlet 108 of the atmospheric pressure bubbling reaction distillation tower 1 is a tangential inlet, which is arranged tangentially and inclined downward on the side wall of the atmospheric pressure bubbling reaction distillation tower 1 along the air inlet direction, so that the protective gas enters tangentially along the oblique downward direction, and the angle between the protective gas inlet 108 and the horizontal direction of the cross section of the atmospheric pressure bubbling reaction distillation tower 1 is 45°.

[0077] The number of the protective gas inlets 108 of the atmospheric pressure bubbling reaction distillation tower 1 is 10, and each protective gas inlet 108 is a tangential inlet. The plurality of protective gas inlets 108 are evenly arranged on the side wall of the atmospheric pressure bubbling reaction distillation tower 1 along the circumferential direction.

[0078] In addition, this embodiment also provides a method for preparing a polyester polyol prepolymer, which adopts the above-mentioned system.

[0079] The method comprises the following steps:

[0080] (1) allowing a protective gas to enter the interior of the atmospheric bubbling reaction distillation tower 1 through a protective gas inlet 108 along a tangential inclination of the side wall thereof, and allowing a raw material for preparing a polyester polyol prepolymer to continuously enter the atmospheric bubbling reaction distillation tower 1 through a first raw material inlet 107, and subjecting the raw material for preparing a polyester polyol prepolymer to a preliminary esterification reaction. After the generated by-products and gaseous substances in the reaction system pass through a first separation packing layer 103, the by-products and protective gas are discharged from the atmospheric bubbling reaction distillation tower 1 through a first gas phase discharge port 105, and the generated preliminary esterification product is discharged from the atmospheric bubbling reaction distillation tower 1 through a first liquid phase discharge port 106;

[0081] The raw materials for preparing the polyester polyol prepolymer include a mixed solution of succinic acid, 1,4-butanediol and a catalyst;

[0082] (2) The preliminary esterification product discharged from the first liquid phase discharge port 106 enters the vacuum temperature rising reaction distillation tower 2 through the second raw material inlet 207 to undergo a pre-polycondensation reaction. The generated by-products and the gas phase substances in the reaction system pass through the second separation packing layer 203. The by-products are discharged from the vacuum temperature rising reaction distillation tower 2 from the second gas phase discharge port 205 and enter the vacuum device. The reaction pressure of the vacuum temperature rising reaction distillation tower 2 is then controlled by the vacuum device. The generated polyester polyol prepolymer is discharged from the second liquid phase discharge port 206.

[0083] Among them, in the raw materials for preparing the polyester polyol prepolymer, the molar ratio of succinic acid to 1,4-butanediol is 1:1.2. The catalyst is tetra-n-butyl titanate. The amount of the catalyst is 200ppm of the mass of succinic acid.

[0084] In step (1), the protective gas used is nitrogen.

[0085] In step (1), the temperature of the initial esterification reaction is 170°C.

[0086] By testing the preliminary esterification product discharged from the first liquid phase discharge port 106, it was found that the esterification rate of step (1) was 99%.

[0087] In step (2), the temperature of the pre-polycondensation reaction is 240° C. and the pressure is 70 kPa.

[0088] Example 2

[0089] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 1.

[0090] The specific steps of the method are basically the same as those of Example 1, except that: the raw materials for preparing the polyester polyol prepolymer include a mixed solution of succinic acid, ethylene glycol and a catalyst, the molar ratio of succinic acid to ethylene glycol is 1:1.1, the catalyst is 1-chloro-3-hydroxy-1,1,3,3-tetrabutoxydistannoxane (CHTD), and the amount of the catalyst is 200 ppm of the mass of succinic acid; in step (1), the temperature of the initial esterification reaction is 180°C; by detecting the initial esterification product discharged from the first liquid phase discharge port 106, it is obtained that the esterification rate of step (1) is 98%; in step (2), a deep esterification reaction and a pre-polycondensation reaction are carried out, and the temperature of the deep esterification reaction and the pre-polycondensation reaction is 220°C and the pressure is 80 kPa.

[0091] Example 3

[0092] This embodiment provides a system for preparing polyester polyol prepolymers. The structure of the system is as follows: Figure 2 shown.

[0093] The system comprises: a normal pressure bubbling reaction distillation tower 1, a reduced pressure temperature reaction distillation tower 2, a polyol storage device 3 and a vacuum device 4.

[0094] The tower body of the atmospheric bubbling reaction distillation tower 1 includes a first separation section 101 and a first reaction section 102 from top to bottom. The first separation section is provided with a first separation packing layer 103 , and the first reaction section is provided with a plurality of first tower plates 104 .

[0095] A first gas phase discharge port 105 is provided at the top of the atmospheric pressure bubbling reaction distillation tower 1, and a first liquid phase discharge port 106 is provided at the bottom of the atmospheric pressure bubbling reaction distillation tower 1; a first raw material inlet 107 is provided at the side wall of the atmospheric pressure bubbling reaction distillation tower, and the first raw material inlet 107 is located in the first reaction section 102; a protective gas inlet 108 is provided at the side wall of the atmospheric pressure bubbling reaction distillation tower, and the protective gas inlet 108 is located below the first reaction section 102.

[0096] The tower body of the vacuum temperature reaction distillation tower 2 includes a second separation section 201 and a second reaction section 202 from top to bottom. The second separation section 201 is provided with a second separation packing layer 203 , and the second reaction section 202 is provided with a plurality of second trays 204 .

[0097] A second gas phase discharge port 205 is provided at the top of the vacuum temperature reaction distillation tower 2, and a second liquid phase discharge port 206 is provided at the bottom of the vacuum temperature reaction distillation tower 2; a second raw material inlet 207 is provided on the side wall of the vacuum temperature reaction distillation tower 2, and the second raw material inlet 207 is located in the second reaction section 202.

[0098] The first liquid phase discharge port 106 of the atmospheric pressure bubbling reaction distillation tower 1 is connected to the second raw material inlet 207 of the vacuum temperature rising reaction distillation tower 2 through a pipeline.

[0099] The spray device 208 is arranged inside the tower body of the vacuum temperature reaction distillation tower 2, and the spray device 208 is arranged above the second separation packing layer 203. The spray device 208 is connected to the polyol storage device 3 through a pipeline, and is used to spray polyol into the vacuum temperature reaction distillation tower 2.

[0100] The spray device 208 at least includes a spray pipe 209 and a nozzle 210 connected to the spray pipe 209, and a polyol feed port is provided on the side wall of the vacuum temperature reaction distillation tower 2, the polyol feed port is located above the second separation packing layer 203 of the vacuum temperature reaction distillation tower 2, and the spray pipe 209 is connected to the polyol feed port. In this embodiment, the spray device 208 is provided in the vacuum temperature reaction distillation tower 2 to facilitate the reflux of the oligomers in the reaction system, the control of the carboxyl content, and the adjustment of the esterification rate or the transesterification rate.

[0101] The tower bodies of the atmospheric bubbling reaction distillation tower 1 and the reduced pressure temperature reaction distillation tower 2 are respectively provided with heating jackets 5 for heating the two reaction distillation towers to the temperature required for the reaction.

[0102] The plurality of first trays 104 in the atmospheric bubbling reaction distillation tower 1 have a multi-stage overflow structure. The plurality of second trays 204 in the vacuum temperature reaction distillation tower 2 also have a multi-stage overflow structure. The first tray 104 and the second tray 204 have the same structure. Specifically, the first tray 104 and the second tray 204 are both inclined hole trays.

[0103] The vacuum device 4 is connected to the second gas phase discharge port 205 of the vacuum temperature-elevating reaction distillation tower 2 through a pipeline, and is used to adjust the pressure of the vacuum temperature-elevating reaction distillation tower 2 to the pressure required for the reaction.

[0104] The packing in the first separation packing layer 103 of the atmospheric bubbling reaction distillation tower 1 is a plate corrugated packing.

[0105] The packing in the second separation packing layer 203 of the vacuum temperature reaction distillation tower 2 is a plate corrugated packing.

[0106] The shielding gas inlet 108 of the atmospheric pressure bubbling reaction distillation tower 1 is a tangential inlet, which is arranged tangentially and obliquely downwardly on the side wall of the atmospheric pressure bubbling reaction distillation tower 1 along the air inlet direction, so that the shielding gas enters tangentially from the oblique downward direction, and the angle between the shielding gas inlet 108 and the horizontal direction of the cross section of the atmospheric pressure bubbling reaction distillation tower 1 is 60°. The shielding gas inlet 108 arranged tangentially and obliquely downward on the side wall of the atmospheric pressure bubbling reaction distillation tower 1 in this embodiment can enable the shielding gas to enter the tower body tangentially and obliquely downward along the side wall of the atmospheric pressure bubbling reaction distillation tower 1 for bubbling, which is beneficial to strengthening material mixing, separation of products and by-products, and avoiding blockage of the shielding gas inlet.

[0107] The number of the protective gas inlets 108 of the atmospheric pressure bubbling reaction distillation tower 1 is 8, and each protective gas inlet 108 is a tangential inlet. The plurality of protective gas inlets 108 are evenly arranged on the side wall of the atmospheric pressure bubbling reaction distillation tower 1 along the circumferential direction.

[0108] In addition, this embodiment also provides a method for preparing a polyester polyol prepolymer, which adopts the above-mentioned system.

[0109] The method comprises the following steps:

[0110] (1) allowing a protective gas to enter the interior of the atmospheric bubbling reaction distillation tower 1 through a protective gas inlet 108 along a tangential inclination of the side wall thereof, and allowing a raw material for preparing a polyester polyol prepolymer to continuously enter the atmospheric bubbling reaction distillation tower 1 through a first raw material inlet 107, and subjecting the raw material for preparing a polyester polyol prepolymer to a preliminary esterification reaction. After the generated by-products and gaseous substances in the reaction system pass through a first separation packing layer 103, the by-products and protective gas are discharged from the atmospheric bubbling reaction distillation tower 1 through a first gas phase discharge port 105, and the generated preliminary esterification product is discharged from the atmospheric bubbling reaction distillation tower 1 through a first liquid phase discharge port 106;

[0111] The raw materials for preparing the polyester polyol prepolymer include a mixed solution of succinic acid, 1,4-butanediol and a catalyst;

[0112] (2) The preliminary esterification product discharged from the first liquid phase discharge port 106 enters the vacuum temperature rising reaction distillation tower 2 through the second raw material inlet 207, and mainly performs deep esterification reaction. The 1,4-butanediol is sprayed into the vacuum temperature rising reaction distillation tower 2 by the spray device 208 in the vacuum temperature rising reaction distillation tower 2 to participate in the reaction. After the generated by-products and the gas phase substances in the reaction system pass through the second separation packing layer 203, the by-products are discharged from the vacuum temperature rising reaction distillation tower 2 from the second gas phase discharge port 205, and enter the vacuum device, and then the reaction pressure of the vacuum temperature rising reaction distillation tower 2 is controlled by the vacuum device. The generated polyester polyol prepolymer is discharged from the second liquid phase discharge port 206.

[0113] Among them, in the raw materials for preparing the polyester polyol prepolymer, the molar ratio of succinic acid to 1,4-butanediol is 1:1.3. The catalyst is tetra-n-butyl titanate. The amount of the catalyst is 5000ppm of the mass of succinic acid.

[0114] In step (1), the protective gas used is nitrogen.

[0115] In step (1), the temperature of the initial esterification reaction is 160°C.

[0116] By testing the preliminary esterification product discharged from the first liquid phase discharge port 106, it was found that the esterification rate of step (1) was 82%.

[0117] In step (2), the mass ratio of 1,4-butanediol sprayed into the vacuum temperature reaction distillation tower by the spray device 208 to the mass ratio of the preliminary esterification product is 0.5.

[0118] In step (2), the temperature of the deep esterification reaction is 180° C. and the pressure is 80 kPa.

[0119] By testing the polyester polyol prepolymer discharged from the second liquid phase discharge port 206, it was found that the esterification rate of step (2) was 99%.

[0120] By testing the substances discharged from the first gas phase outlet 105 and the second gas phase outlet 205, it was found that the entrained amount of diols and oligomers in the gas phase of steps (1) and (2) was less than 1%.

[0121] In this embodiment, the generated by-products mainly include water and tetrahydrofuran, and the gas phase substances in the reaction system mainly include 1,4-butanediol and oligomers generated by the reaction, etc. These gas phase substances can be separated and refluxed from 1,4-butanediol and oligomers generated by the reaction in time through the first separation packing layer 103 or the second separation packing layer 203, while the by-products water and tetrahydrofuran are purified and discharged from the top of the tower. The by-products discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205 are mainly aqueous solutions of tetrahydrofuran, and the aqueous solutions of tetrahydrofuran discharged from the two reaction distillation towers can be mixed and then enter the tetrahydrofuran refining system for refining.

[0122] Example 4

[0123] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 3.

[0124] The specific steps of the method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 170°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is found that the esterification rate of step (1) is 85%; in step (2), a deep esterification reaction and a pre-polycondensation reaction are carried out at a temperature of 205°C and a pressure of 50 kPa. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is found that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 0.8%.

[0125] Example 5

[0126] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 3.

[0127] The specific steps of the method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 210°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is found that the esterification rate of step (1) is 90%; in step (2), a deep esterification reaction and a pre-polycondensation reaction are carried out at a temperature of 225°C and a pressure of 100 kPa. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is found that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 2%.

[0128] Example 6

[0129] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 3.

[0130] The specific steps of the method are basically the same as those of Example 3, except that: the raw materials for preparing the polyester polyol prepolymer include a mixed solution of dimethyl succinate, 1,4-butanediol and a catalyst, the molar ratio of dimethyl succinate to 1,4-butanediol is 1:1.1, the catalyst is tetra-n-butyl titanate, and the amount of the catalyst is 5000 ppm of the mass of dimethyl succinate; in step (1), the temperature of the initial ester exchange reaction is 130°C; by detecting the initial ester exchange product discharged from the first liquid phase discharge port 106, it is obtained that the ester exchange rate of step (1) is 80%; in step (2), a deep esterification reaction is mainly carried out, the temperature of the deep ester exchange reaction is 150°C, and the pressure is 15 kPa; by detecting the polyester polyol prepolymer discharged from the second liquid phase discharge port 206, it is obtained that the esterification rate of step (2) is 98%. By testing the substances discharged from the first gas phase outlet 105 and the second gas phase outlet 205, it was found that the entrained amount of diols and oligomers in the gas phase of steps (1) and (2) was less than 2%.

[0131] Example 7

[0132] This embodiment provides a system for preparing polyester polyol prepolymers. The system is substantially the same as the system provided in Example 3, except that the angle between the protective gas inlet 108 and the horizontal direction of the cross section of the atmospheric bubbling reaction distillation tower 1 is 15°.

[0133] This embodiment also provides a method for preparing a polyester polyol prepolymer, which adopts the system of this embodiment. The specific steps of this method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 260°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is obtained that the esterification rate of step (1) is 92%; in step (2), the mass ratio of 1,4-butanediol sprayed into the vacuum temperature rising reaction distillation tower by the spray device 208 to the mass ratio of the preliminary esterification product is 0.02; deep esterification reaction and pre-polycondensation reaction are carried out at a temperature of 205°C and a pressure of 50kPa. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is obtained that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 1%.

[0134] Example 8

[0135] This embodiment provides a system for preparing polyester polyol prepolymers. The system is substantially the same as the system provided in Example 3, except that the angle between the protective gas inlet 108 and the horizontal direction of the cross section of the atmospheric bubbling reaction distillation tower 1 is 85°.

[0136] This embodiment also provides a method for preparing a polyester polyol prepolymer, which adopts the system of this embodiment. The specific steps of this method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 210°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is obtained that the esterification rate of step (1) is 90%; in step (2), the mass ratio of 1,4-butanediol sprayed into the vacuum temperature rising reaction distillation tower by the spray device 208 to the mass ratio of the preliminary esterification product is 5; deep esterification reaction and pre-polycondensation reaction are carried out at a temperature of 260°C and a pressure of 101.325 kPa. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is obtained that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 3%.

[0137] Example 9

[0138] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 3.

[0139] The specific steps of the method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 200°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is obtained that the esterification rate of step (1) is 88%; in step (2), the mass ratio of 1,4-butanediol sprayed into the vacuum temperature rising reaction distillation tower by the spray device 208 to the mass ratio of the preliminary esterification product is 0.2; the deep esterification reaction is mainly carried out, and the temperature of the deep esterification reaction is 180°C and the pressure is 100 kPa; by detecting the polyester polyol prepolymer discharged from the second liquid phase discharge port 206, it is obtained that the esterification rate of step (2) is 98%. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is obtained that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 2%.

[0140] Example 10

[0141] This embodiment provides a method for preparing a polyester polyol prepolymer, which adopts the system for preparing a polyester polyol prepolymer provided in Example 3.

[0142] The specific steps of the method are basically the same as those of Example 3, except that: in step (1), the temperature of the preliminary esterification reaction is 140°C; by detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is obtained that the esterification rate of step (1) is 81%; in step (2), the mass ratio of 1,4-butanediol sprayed into the vacuum temperature reaction distillation tower by the spray device 208 to the mass ratio of the preliminary esterification product is 2; deep esterification reaction and pre-polycondensation reaction are carried out at a temperature of 240°C and a pressure of 50 kPa. By detecting the substances discharged from the first gas phase discharge port 105 and the second gas phase discharge port 205, it is obtained that the entrainment of diols and oligomers in the gas phase of steps (1) and (2) is less than 3%.

[0143] Comparative Example 1

[0144] This comparative example provides a system for preparing polyester polyol prepolymer, which is different from Example 3 in that: the tower body of the vacuum temperature reaction distillation tower 2 is not provided with a spraying device 208 for spraying polyol. The polyester polyol prepolymer is prepared by the method in Example 3. By detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is found that the esterification rate of step (1) is 82%; by detecting the polyester polyol prepolymer discharged from the second liquid phase discharge port 206, it is found that the esterification rate of step (2) is 96%; by detecting the material discharged from the second gas phase discharge port 205, it is found that the entrainment of diols and oligomers in the gas phase of step (2) is greater than 5%.

[0145] Comparative Example 2

[0146] This comparative example provides a system for preparing polyester polyol prepolymer, which is different from Example 3 in that: the atmospheric bubbling reaction distillation tower 1 is not provided with the first separation packing layer 103; the reduced pressure temperature reaction distillation tower 2 is not provided with the second separation packing layer 203 and the spraying device 208 for spraying polyol. The polyester polyol prepolymer is prepared by the method in Example 3. By detecting the preliminary esterification product discharged from the first liquid phase discharge port 106, it is found that the esterification rate of step (1) is 82%; by detecting the polyester polyol prepolymer discharged from the second liquid phase discharge port 206, it is found that the esterification rate of step (2) is 93%; by detecting the material discharged from the first gas phase discharge port 105, it is found that the entrainment amount of diols and oligomers in the gas phase of step (1) is greater than 8%; by detecting the material discharged from the second gas phase discharge port 205, it is found that the entrainment amount of diols and oligomers in the gas phase of step (2) is greater than 10%.

Claims

1. A system for preparing a polyester polyol prepolymer, the system comprising: Atmospheric pressure bubbling reaction distillation tower and vacuum temperature rising reaction distillation tower; The tower body of the atmospheric bubbling reaction distillation tower includes a first separation section and a first reaction section from top to bottom, the first separation section is provided with a first separation packing layer, and the first reaction section is provided with a plurality of tower trays; The atmospheric bubbling reaction distillation tower is provided with a first gas phase discharge port, a first liquid phase discharge port, a first raw material inlet and a protective gas inlet; The tower body of the vacuum temperature-raising reaction distillation tower includes a second separation section and a second reaction section from top to bottom, the second separation section is provided with a second separation packing layer, and the second reaction section is provided with a plurality of tower trays; The vacuum temperature reaction distillation tower is provided with a second gas phase discharge port, a second liquid phase discharge port and a second raw material inlet; The first liquid phase discharge port of the atmospheric pressure bubbling reaction distillation tower is connected to the second raw material inlet of the vacuum temperature rising reaction distillation tower through a pipeline.

2. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The system further comprises: a polyol storage device, and the vacuum temperature reaction distillation tower further comprises a spray device; the spray device is arranged inside the tower body of the vacuum temperature reaction distillation tower, and the spray device is arranged above the second separation packing layer; the spray device is connected to the polyol storage device through a pipeline, and is used to spray polyol into the vacuum temperature reaction distillation tower; Preferably, the spray device comprises at least a spray pipe and a nozzle connected to the spray pipe, and a polyol feed port is provided on the side wall of the vacuum temperature rising reaction distillation tower, the polyol feed port is located above the second separation packing layer of the vacuum temperature rising reaction distillation tower, and the spray pipe is connected to the polyol feed port.

3. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The tower bodies of the atmospheric pressure bubbling reaction distillation tower and the reduced pressure temperature reaction distillation tower are respectively provided with heating jackets on their exteriors.

4. The system for preparing polyester polyol prepolymer according to claim 1, wherein: Several trays in the atmospheric bubbling reaction distillation tower and the vacuum temperature rising reaction distillation tower have a multi-stage overflow structure; Preferably, the tower tray comprises one or a combination of inclined hole tower tray, bubble cap tower tray, fixed valve tower tray and vertical sieve plate tower tray; More preferably, the tower tray is an inclined hole tower tray.

5. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The system further comprises: a vacuum device, which is connected to the second gas phase discharge port of the vacuum temperature rising reaction distillation tower through a pipeline.

6. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The filler in the first separation filler layer of the atmospheric bubbling reaction distillation tower is a random filler or a structured filler; The filler in the second separation filler layer of the vacuum temperature rising reaction distillation tower is a random filler or a structured filler.

7. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The top of the atmospheric pressure bubbling reaction distillation tower is provided with the first gas phase discharge port; the bottom of the atmospheric pressure bubbling reaction distillation tower is provided with the first liquid phase discharge port; the side wall of the atmospheric pressure bubbling reaction distillation tower is provided with the first raw material inlet, and the first raw material inlet is located in the first reaction section; the side wall of the atmospheric pressure bubbling reaction distillation tower is provided with the protective gas inlet, and the protective gas inlet is located below the first reaction section.

8. The system for preparing polyester polyol prepolymer according to claim 1, wherein: The top of the vacuum temperature rising reaction distillation tower is provided with the second gas phase discharge port; the bottom of the vacuum temperature rising reaction distillation tower is provided with the second liquid phase discharge port; the side wall of the vacuum temperature rising reaction distillation tower is provided with the second raw material inlet, and the second raw material inlet is located in the second reaction section.

9. The system for preparing polyester polyol prepolymer according to claim 7, wherein: The protective gas inlet of the atmospheric bubbling reaction distillation tower is a tangential inlet, which is tangential to the side wall of the atmospheric bubbling reaction distillation tower; Preferably, the protective gas inlet of the atmospheric pressure bubbling reaction distillation tower is arranged tangentially and obliquely downward on the side wall of the atmospheric pressure bubbling reaction distillation tower along the air inlet direction, so that the protective gas enters tangentially along the oblique downward direction, and the angle between the protective gas inlet and the horizontal direction of the cross section of the atmospheric pressure bubbling reaction distillation tower is 15 to 85°.

10. The system for preparing polyester polyol prepolymer according to claim 9, wherein: The atmospheric pressure bubbling reaction distillation tower has a plurality of protective gas inlets, each of which is a tangential inlet. The plurality of protective gas inlets are uniformly arranged along the circumferential direction on the side wall of the atmospheric pressure bubbling reaction distillation tower.

11. A method for preparing a polyester polyol prepolymer, the method using a system for preparing a polyester polyol prepolymer according to any one of claims 1 to 10, the method comprising the following steps: (1) allowing a protective gas to enter an atmospheric pressure bubbling reaction distillation tower, and allowing a raw material for preparing a polyester polyol prepolymer to enter the atmospheric pressure bubbling reaction distillation tower, the raw material for preparing a polyester polyol prepolymer undergoes a preliminary esterification or transesterification reaction, the generated by-products and gaseous substances in the reaction system pass through a first separation filler layer, the by-products and protective gas are discharged from the atmospheric pressure bubbling reaction distillation tower from a first gas phase discharge port, and the generated preliminary esterification or transesterification products are discharged from the atmospheric pressure bubbling reaction distillation tower from a first liquid phase discharge port; (2) The preliminary esterification or transesterification product discharged from the first liquid phase discharge port enters a vacuum temperature reaction distillation tower to undergo one or more of a deep esterification reaction, a transesterification reaction, and a pre-polycondensation reaction. After the generated by-products and the gas phase substances in the reaction system pass through a second separation packing layer, the by-products are discharged from the vacuum temperature reaction distillation tower from the second gas phase discharge port, and the generated polyester polyol prepolymer is discharged from the second liquid phase discharge port.

12. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: In step (1), the raw materials for preparing the polyester polyol prepolymer include a mixed solution of one or a combination of polycarboxylic acids and their derivatives, polyols and a catalyst.

13. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: In step (1), the protective gas is directed downwardly into the interior of the tower along the tangential direction of the side wall of the atmospheric pressure bubbling reaction distillation tower; In step (1), the raw materials for preparing the polyester polyol prepolymer are continuously fed into a normal pressure bubbling reaction distillation tower.

14. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: In step (1), the temperature of the preliminary esterification or transesterification reaction is 130 to 260°C, preferably 140 to 200°C.

15. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: Step (2) further comprises: spraying the polyol into the vacuum temperature reaction distillation tower using a spray device in the vacuum temperature reaction distillation tower; Preferably, the mass ratio of the polyol sprayed into the vacuum temperature reaction distillation tower by the spray device to the preliminary esterification or transesterification product is 0.02-5.

16. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: In step (2), the temperature of one or more of the deep esterification reaction, transesterification reaction and pre-polycondensation reaction is 150-260°C, preferably 180-240°C.

17. The method for preparing a polyester polyol prepolymer according to claim 11, wherein: In step (2), the pressure of one or more of the deep esterification reaction, transesterification reaction and pre-polycondensation reaction is 15 to 101.325 kPa, preferably 50 to 100 kPa.

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