A separation system and method of transesterification steam for transesterification process of preparing PBS

Abstract

The application discloses a transesterification steam separation system and method for preparing PBS by a transesterification method. The separation system comprises a transesterification reactor (101), a material recycling column (111), a methanol recovery column (121), an extraction column (131), a water separation column (141), an atmospheric separation column (151) and a pressurized separation column (161). The application designs a separation and refining production line according to different characteristics and uses of complex components in the transesterification steam for preparing PBS by the transesterification method. According to process requirements, relevant materials are recycled, and the materials are cyclically refined without introducing external substances, so that the product yield is improved, 98.5% of methanol and more than 99.5% of high-purity tetrahydrofuran are obtained, energy optimization is performed, and the effect of energy saving and consumption reduction is achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, specifically to a separation system and method for transesterification vapor in the preparation of PBS by transesterification. Background Technology

[0002] Biodegradable plastics are a class of plastics that can degrade into environmentally harmless substances under natural conditions after use, and are considered one of the effective ways to solve "white pollution." Polybutylene succinate (PBS) does not contain benzene rings in its structure and has good degradability, making it a fully biodegradable plastic with excellent overall performance.

[0003] Currently, PBS is mainly prepared by direct esterification polymerization of succinic acid and butanediol (CN115109237A). This method has problems such as high production cost of the main raw material succinic acid, strong acidity of succinic acid, high corrosiveness of the complete production process to the reaction equipment, and large amount of tetrahydrofuran by-product.

[0004] PBS is prepared via transesterification using dimethyl succinate and butanediol as raw materials. The process involves transesterification, pre-polymerization, and polymerization. This route utilizes the low acidity of dimethyl succinate, which addresses the corrosiveness of succinic acid in existing direct esterification processes. Furthermore, it effectively reduces the formation of tetrahydrofuran from butanediol during polymerization. PBS produced via transesterification exhibits superior quality, meeting the requirements of downstream products in terms of color, viscosity, terminal carboxyl groups, and antioxidant properties.

[0005] However, the separation products in the transesterification stage of the transesterification process are quite complex. Besides methanol produced from the reaction of dimethyl succinate and butanediol, the esterification vapor contains a large number of other components, including tetrahydrofuran and water generated from the dehydration of butanediol, as well as dimethyl succinate, butanediol, and oligomers carried over in the gas phase. Methanol, tetrahydrofuran, and water form an azeotropic mixture, making separation difficult, and the main substances need to be recovered or reused. Therefore, a scientifically designed separation and purification process is required to maximize the recycling and purification of materials in the complex process while ensuring the separation objectives, guaranteeing the purity and recovery rate of each component, and ensuring energy recycling. Summary of the Invention

[0006] The purpose of this invention is to provide a separation system and method for transesterification vapor in the preparation of PBS using the transesterification method. This invention addresses the diverse characteristics of the complex components contained in the transesterification vapor of PBS prepared by the transesterification method, designing a purification production line and purification process. Based on target requirements, the corresponding materials are recycled and purified in a circular manner, and energy utilization is optimized, resulting in energy saving and consumption reduction.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] The present invention provides a separation system for transesterification vapor in the preparation of PBS by transesterification. The separation system includes: a transesterification reactor, a material recycling tower, a methanol recovery tower, an extraction tower, a water separation tower, an atmospheric pressure separation tower, and a pressurized separation tower.

[0009] The top of the transesterification reactor is connected to the feed inlet in the middle of the material recycling tower. The transesterification vapor generated in the transesterification reactor enters the material recycling tower through the feed inlet. The bottom of the material recycling tower is connected to the top of the transesterification reactor. The recombinant obtained at the bottom of the tower is divided into dimethyl succinate, butanediol and some oligomers, which are returned to the transesterification reactor for further reaction or discharged and collected as needed.

[0010] The top of the material recycling tower is connected in sequence to condenser A and reflux tank A, and then returns to the top to form a circulation loop; the outlet of reflux tank A is also connected to condensate tank, and the outlet of condensate tank is connected to the feed inlet in the middle of the methanol recovery tower; methanol, water and light components such as tetrahydrofuran are obtained at the top of the material recycling tower, and the gas phase components separated at the top of the tower are collected in condensate tank after condensation, and then transported to the methanol recovery tower;

[0011] The top of the methanol recovery tower is connected in sequence to condenser B and reflux tank B, and then returns to the top to form a circulation loop; the outlet of reflux tank B is also connected to the feed inlet in the middle of the extraction tower; after being processed by the methanol recovery tower, the top vapor mainly contains tetrahydrofuran, methanol and water, and after condensation, it enters the middle of the extraction tower, and the bottom of the tower is purified to remove excess methanol (purity > 98%) and collected.

[0012] The top of the extraction tower is sequentially connected to a condenser C and a reflux tank C, which then return to the top to form a circulation loop. The outlet of the reflux tank C is also connected to the feed inlet in the middle of the atmospheric pressure separation tower. The upper part of the extraction tower is provided with a water inlet, and the bottom is connected to the feed inlet in the middle of the water separation tower. Water is added from the top of the extraction tower as an extractant to extract and distill the material entering the middle section. Methanol and extractant-water are obtained at the bottom, which enter the water separation tower to separate water. A tetrahydrofuran aqueous solution of a certain concentration is obtained at the top of the extraction tower and enters the atmospheric pressure separation tower for further separation.

[0013] The top of the water separation tower is connected in sequence to a condenser D and a reflux tank D, and then returns to the top to form a circulation loop; the outlet of the reflux tank D is also connected to the condensate tank; methanol and tetrahydrofuran are separated at the top of the water separation tower, and after condensation, they are transported to the condensate tank for repeated purification, and the bottom of the tower is water;

[0014] The top of the atmospheric pressure separation tower is connected to a condenser E and a reflux tank E in sequence, and then returns to the top to form a circulation loop; the outlet of the reflux tank E is also connected to the feed inlet in the middle of the pressurized separation tower; the tetrahydrofuran aqueous solution of a certain concentration obtained after extraction and separation in the extraction tower enters the atmospheric pressure separation tower for separation, and the top yields an atmospheric pressure azeotrope of tetrahydrofuran and water, which enters the pressurized separation tower for further separation; the bottom yields wastewater, which is collected.

[0015] The top of the pressurized separation tower is connected in sequence to a condenser F and a reflux tank F, which then return to the top to form a circulation loop. The outlet of the reflux tank F is also connected to the middle of the atmospheric pressure separation tower. The atmospheric pressure azeotrope of tetrahydrofuran and water is separated in the pressurized separation tower. Tetrahydrofuran is obtained at the bottom of the tower, and the pressurized azeotrope of tetrahydrofuran and water is separated at the top of the tower. After condensation, it returns to the atmospheric pressure separation tower for further distillation separation.

[0016] According to the system of the present invention, preferably, the bottom of the water separation tower is connected to the inlet of the upper part of the extraction tower, and the water at the bottom of the tower is returned to the upper part of the extraction tower for recycling as an extractant.

[0017] According to the system of the present invention, preferably, the bottom of the material recycling tower, methanol recovery tower, extraction tower, water separation tower, and atmospheric pressure separation tower are all equipped with reboilers for heating and reboiling the bottom material. The heating medium of the material recycling tower is preferably liquid / gas phase heat transfer oil, but other heating media may also be used.

[0018] According to the system of the present invention, preferably, the bottom outlet of the pressurized separation tower is connected to an external circulating reboiler, and then returns to the bottom to form a circulation loop; and the bottom outlet of the pressurized separation tower is also connected to the hot side of the bottom heat exchanger, after which tetrahydrofuran material is output for collection; the outlet of the reflux tank E is connected to the feed inlet in the middle of the pressurized separation tower after passing through the cold side of the bottom heat exchanger. The material in the reflux tank E exchanges heat with the material at the bottom of the pressurized separation tower for preheating before entering the pressurized separation tower.

[0019] More preferably, the external circulation reboiler adopts a siphon heating method, and the heat medium is preferably steam at 0.1 to 3 MPa, but other heating media may also be used.

[0020] According to the system of the present invention, preferably, a material recycling pump, a three-way valve, and a flow control valve are sequentially installed on the pipeline connecting the bottom of the material recycling tower to the top of the transesterification reactor. The heavy components (dimethyl succinate, butanediol, and some oligomers) obtained from the bottom of the material recycling tower are collected by the material recycling pump, diverted by the three-way valve, and, depending on the reaction conditions, part of them are returned to the transesterification reactor for further reaction under the control of the flow control valve, while the rest are collected.

[0021] According to the system of the present invention, preferably, the material recycling tower is a negative pressure distillation tower and the pressurized separation tower is a pressurized distillation tower.

[0022] According to the system of the present invention, preferably, the material recycling tower includes a tower body, the tower body including a rectification section in the upper section and a stripping section in the lower section;

[0023] The rectifying section contains structured packing; the stripping section is equipped with several large-aperture guide plates. These guide plates have guide holes and sieve holes. A portion of the guide hole's edge extends obliquely upwards, protruding and covering at least a part of the guide hole, acting as a guide plate. An opening is formed between the guide plate and the guide hole, parallel to the surface of the large-aperture guide plate. This allows the gaseous stream entering from below to change direction after passing through the guide hole, ultimately aligning with the flow direction of the liquid phase on the large-aperture guide plate. The rising gaseous stream from the lower large-aperture guide plate cuts and decomposes the liquid phase near the guide hole into multiple micro-units through the guide hole, facilitating mass transfer and improving the column's separation efficiency. The gas inlet and outlet ends of the guide holes are designed with a certain curvature to reduce airflow resistance, increase mass transfer efficiency, and prevent the formation of dead zones on the plates, which could lead to oligomer deposition and blockage in the ester exchange liquid. The sieve holes are used to allow the rising gaseous stream to pass through.

[0024] According to the system of the present invention, preferably, an overflow weir and a downcomer are respectively provided on the upper and lower sides of the notch edge of the large-diameter guide plate.

[0025] According to the system of the present invention, preferably, the height of the overflow weir is 5 to 45 mm; the radial cross-section of the large-aperture guide tower plate is an arc parallel to the side wall of the tower body, and the large-aperture guide tower plate extends downward in a stepped manner with the arc diameter increasing progressively.

[0026] According to the system of the present invention, preferably, the aperture of the sieve holes is 5-16 mm, and the opening ratio is 5-13%.

[0027] According to the system of the present invention, preferably, the theoretical number of large-aperture guide trays in the stripping section accounts for 10% to 50% of the total number of trays, more preferably 20% to 40%;

[0028] The theoretical number of trays in the rectification section accounts for 50% to 90% of the total number of trays, more preferably 60% to 80%.

[0029] Another aspect of the present invention provides a method for separating transesterification vapors in the preparation of PBS by transesterification, wherein the separation method is performed using any of the above-described systems.

[0030] Specifically, the process includes the following:

[0031] The transesterification vapor generated in the transesterification reactor enters the material recycling tower. The heavy components obtained at the bottom of the tower (dimethyl succinate, butanediol and some oligomers) are returned to the transesterification reactor for further reaction or discharged and collected as needed. The gaseous components separated at the top of the tower (methanol, water and light components such as tetrahydrofuran) are condensed and collected in the condensate tank, and then transported to the methanol recovery tower.

[0032] After being processed by the methanol recovery tower, the vapor at the top of the tower (mainly containing tetrahydrofuran, methanol and water) is condensed and enters the middle of the extraction tower. The bottom of the tower is purified to remove excess methanol (purity > 98%) and collected.

[0033] Water is added as the extractant from the top of the extraction tower to extract and distill the material entering the middle section. Methanol and extractant-water are obtained at the bottom of the tower and enter the water separation tower. Methanol and tetrahydrofuran are separated at the top of the water separation tower and then condensed and sent to the condensate tank for repeated purification. Water is obtained at the bottom of the water separation tower. A tetrahydrofuran aqueous solution of a certain concentration is obtained at the top of the extraction tower and enters the atmospheric pressure separation tower. An atmospheric pressure azeotrope of tetrahydrofuran and water is obtained at the top of the atmospheric pressure separation tower and then condensed and entered into the pressure separation tower. Wastewater is obtained at the bottom of the pressure separation tower.

[0034] The atmospheric pressure azeotrope of tetrahydrofuran and water is separated in a pressure separation column. Tetrahydrofuran is obtained at the bottom of the column, while the pressure azeotrope of tetrahydrofuran and water is separated at the top of the column. After condensation, it is returned to the atmospheric pressure separation column for further distillation.

[0035] Tetrahydrofuran and methanol are difficult to separate under normal conditions. This invention sets up an extraction tower and uses water as the extractant. No foreign impurities are introduced during the extractive distillation. At the same time, the extract obtained by extractive distillation is separated by a water separation tower. The separated methanol is recycled and purified. The water obtained at the bottom of the tower can be returned to the extraction tower as an extractant for reuse. Through this method and design, complete recovery of methanol and reuse of water during the extraction process are ensured in the entire separation system.

[0036] According to the method of the present invention, preferably, the water at the bottom of the water separation tower is returned to the upper part of the extraction tower for recycling as an extractant.

[0037] According to the method of the present invention, preferably, the tetrahydrofuran and water azeotrope obtained at the top of the atmospheric pressure separation tower is preheated by heat exchange with the bottom material of the pressurized separation tower after condensation, and then enters the pressurized separation tower.

[0038] According to the method of the present invention, preferably, the heavy components (dimethyl succinate, butanediol and some oligomers) obtained from the bottom of the material recycling tower are collected by the material recycling pump, and after being diverted by a three-way valve, part of them are returned to the transesterification reactor for further reaction under the control of the flow control valve, and part of them are collected.

[0039] According to the method of the present invention, preferably, the top temperature of the material recycling tower is 85-105°C to ensure complete removal of low-boiling-point components; the bottom temperature is 185-235°C; the operating pressure is 0.6-1.3 bar (absolute pressure); and the reflux ratio is 0.3-4.

[0040] According to the method of the present invention, preferably, the methanol recovery tower has a top temperature of 55–65°C, an operating pressure of atmospheric pressure to 1.2 bar (absolute pressure), a bottom temperature of 60–70°C, and a reflux ratio of 0.5–20. Through this separation process, a purified mixture mainly composed of tetrahydrofuran, methanol, and water is obtained from the top of the tower.

[0041] According to the method of the present invention, preferably, the top temperature of the extraction column is 55-70°C, the operating pressure is atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is 69-85°C, the reflux ratio is 0.5-30, and the ratio of the flow rate of the extractant water to the flow rate of the material entering the middle section is 3:1 to 1:2, to ensure the effective separation of tetrahydrofuran and methanol.

[0042] According to the method of the present invention, preferably, the top temperature of the water separation tower is 55-70°C, the operating pressure is atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is 90-110°C, and the reflux ratio is 1-5.

[0043] According to the method of the present invention, preferably, the top temperature of the atmospheric pressure separation column is 55-70°C, the operating pressure is atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is 90-110°C, and the reflux ratio is 0.5-5.

[0044] According to the method of the present invention, preferably, the top temperature of the pressurized separation tower is 95–130°C, the operating pressure is 3–12 bar (absolute pressure), the bottom temperature is 110–140°C, and the reflux ratio is 1–15. Under these process conditions, the separation efficiency of tetrahydrofuran and aqueous solution by pressure swing separation is guaranteed, while keeping the manufacturing and operating costs of the device within a reasonable and scientific range.

[0045] According to the method of the present invention, preferably, the content of methanol and water in the heavy components obtained from the bottom of the material recycling tower is less than 0.1%, of which water is less than 800 ppm; on the basis of ensuring the recycling of the returned material, the original transesterification reaction is not affected, and the reaction material ratio of transesterification is guaranteed.

[0046] According to the method of the present invention, preferably, the methanol obtained at the bottom of the methanol recovery tower has a purity greater than 98 wt%, which can ensure the effective recycling of methanol.

[0047] According to the method of the present invention, preferably, the methanol content in the tetrahydrofuran aqueous solution obtained at the top of the extraction tower is less than 0.1 wt%, which ensures the purity of the final tetrahydrofuran product in the subsequent tetrahydrofuran separation process.

[0048] According to the method of the present invention, preferably, the water at the bottom of the water separation tower has a purity greater than 99 wt% and can be returned to the extraction tower as an extractant for reuse. The mixture of tetrahydrofuran and methanol with a water content of less than 1% is separated at the top of the tower and returned to the condensate tank for recycling and purification, thus ensuring the effective utilization of the material.

[0049] According to the method of the present invention, preferably, the tetrahydrofuran obtained at the bottom of the pressurized separation tower is qualified tetrahydrofuran with a concentration greater than 99.5 wt%.

[0050] The beneficial effects of this invention include:

[0051] 1) This invention addresses the complex components contained in the transesterification vapor of poly(dimethyl succinate) (PBS) prepared by transesterification using dimethyl succinate and butanediol as raw materials, and the azeotropic properties of multiple components. A refining production process and corresponding matching system were designed to effectively separate the components in the transesterification vapor according to the new process requirements, obtain qualified reaction reclaimed materials, effectively control the amount of reclaimed materials, optimize the transesterification reaction process and material ratio, and obtain products with greater than 98% methanol and 99.5 wt% tetrahydrofuran.

[0052] 2) The material recycling tower of the present invention is designed with different types of rectification section and stripping section. The upper part of the rectification section adopts high-efficiency packing design, and the stripping section adopts large-diameter guide plate design. Through the scientific design of guide holes and sieve holes, the device has high separation efficiency and anti-clogging performance. The high-efficiency large-diameter guide plate of the stripping section is easier to clean.

[0053] 3) In the process design route of this invention, based on the material characteristics, the entire separation process does not introduce new media, and can also realize the repeated purification of materials and the recycling of energy. Based on the reuse of materials, it has significant energy saving and consumption reduction effects. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the system and process flow according to a preferred embodiment of the present invention.

[0055] Figure 2 This is a schematic diagram of the system and process flow for Comparative Example 1, which involves first performing pressurized separation and then atmospheric pressure separation.

[0056] Figure 3 This is a schematic diagram of the system and process flow for Comparative Example 2, where methanol pre-dehydration was not performed and extraction and separation were carried out directly.

[0057] Figure 4 This is a schematic diagram of the structure of a material recycling tower according to the present invention.

[0058] Figure 5 This is a schematic diagram of the guide hole structure of the material recycling tower in this invention.

[0059] Figure 6 This is a schematic diagram of a large-diameter guide plate structure for a material recycling tower according to the present invention.

[0060] Explanation of reference numerals in the attached figures:

[0061] 101. Ester exchange reactor; 102. Material recycling pump; 103. Three-way valve; 104. Flow control valve.

[0062] 111. Material recycling tower; 112. Condenser A; 113. Reflux tank A; 114. Condensate tank; 115. Reboiler.

[0063] 121. Methanol recovery tower; 122. Condenser B; 123. Reflux tank B;

[0064] 131. Extraction tower; 132. Condenser C; 133. Reflux tank C;

[0065] 141. Water separation tower; 142. Condenser D; 143. Reflux tank D;

[0066] 151. Atmospheric pressure separation tower; 152. Condenser E; 153. Reflux tank E;

[0067] 161. Pressurized separation tower; 162. Condenser F; 163. Reflux tank F; 164. External circulation reboiler; 165. Tower bottom heat exchanger.

[0068] 400. Tower body; 401. Feed inlet; 402. Top vapor outlet; 403. Bottom liquid outlet; 404. Rectifying section; 405. Stripping section; 406. Structured packing; 407. Large-aperture guide plate; 408. Downcomer; 409. Overflow weir; 410. Guide plate; 411. Guide hole; 412. Liquid phase; 416. Sieve hole. Detailed Implementation

[0069] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0070] This invention provides a separation system for transesterification vapor in the preparation of PBS via transesterification, such as... Figure 1As shown, the separation system includes: an ester exchange reactor 101, a material recycling tower 111, a methanol recovery tower 121, an extraction tower 131, a water separation tower 141, an atmospheric pressure separation tower 151, and a pressurized separation tower 161.

[0071] The top of the transesterification reactor 101 is connected to the feed inlet in the middle of the material recycling tower 111. The transesterification vapor generated in the transesterification reactor 101 enters the material recycling tower 111 through the feed inlet. The bottom of the material recycling tower 111 is connected to the top of the transesterification reactor 101. The heavy components obtained at the bottom of the tower are dimethyl succinate, butanediol, and some oligomers, which are returned to the transesterification reactor 101 for further reaction or discharged for collection as needed. Preferably, a material recycling pump 102, a three-way valve 103, and a flow control valve 104 are sequentially installed on the pipeline connecting the bottom of the material recycling tower 111 to the top of the transesterification reactor 101. The heavy components dimethyl succinate, butanediol, and some oligomers obtained at the bottom of the material recycling tower 111 are collected by the material recycling pump 102, diverted by the three-way valve 103, and, depending on the reaction conditions, part of them are returned to the transesterification reactor 101 for further reaction under the control of the flow control valve 104, while the rest are collected.

[0072] Preferably, the material recycling tower 111 is equipped with a reboiler 115 at the bottom for heating the bottom material. The heating medium is preferably liquid / gas-phase heat transfer oil, but other heating media may also be used. In addition, the methanol recovery tower 121, extraction tower 131, water separation tower 141, and atmospheric pressure separation tower 151 are also preferably equipped with reboilers at the bottom, and the heating medium is preferably steam.

[0073] The top of the material recycling tower 111 is sequentially connected to a condenser A112 and a reflux tank A113, and then returns to the top to form a circulation loop. The outlet of the reflux tank A113 is also connected to a condensate tank 114, and the outlet of the condensate tank 114 is connected to the feed inlet in the middle of the methanol recovery tower 121. The top of the material recycling tower 111 obtains methanol, water, and light components such as tetrahydrofuran. The gaseous components separated at the top of the tower are condensed and collected in the condensate tank 114, and then transported to the methanol recovery tower 121.

[0074] The top of the methanol recovery tower 121 is connected in sequence to the condenser B122 and the reflux tank B123, and then returns to the top to form a circulation loop; the outlet of the reflux tank B123 is also connected to the feed inlet in the middle of the extraction tower 131; after being processed by the methanol recovery tower 121, the top vapor mainly contains tetrahydrofuran, methanol and water, and after condensation, it enters the middle of the extraction tower 131, and the bottom of the tower is purified to remove excess methanol (purity > 98%) and collected.

[0075] The top of the extraction tower 131 is sequentially connected to a condenser C132 and a reflux tank C133, which then returns to the top to form a circulation loop. The outlet of the reflux tank C133 is also connected to the feed inlet in the middle of the atmospheric pressure separation tower 151. The upper part of the extraction tower 131 is provided with a water inlet, and the bottom is connected to the feed inlet in the middle of the water separation tower 141. Water is added from the top of the extraction tower 131 as the extractant, and the material entering the middle section undergoes extractive distillation. Methanol and extractant-water are obtained at the bottom, which enter the water separation tower 141 to separate water. A tetrahydrofuran aqueous solution of a certain concentration is obtained at the top of the extraction tower 131, which enters the atmospheric pressure separation tower 151 for further separation. Preferably, the bottom of the water separation tower 141 is connected to the water inlet at the top of the extraction tower 131, and the water at the bottom of the tower is returned to the upper part of the extraction tower 131 for recycling as the extractant.

[0076] Tetrahydrofuran and methanol are difficult to separate under normal conditions. This invention sets up an extraction tower 131 and uses water as the extractant. No foreign impurities are introduced during the extractive distillation. At the same time, the extract obtained by extractive distillation is separated by a water separation tower 141. The separated methanol is recycled and purified, and the water obtained at the bottom of the tower can be returned to the extraction tower 131 as an extractant for reuse. Through this method and design, complete recovery of methanol and reuse of water during the extraction process are ensured in the entire separation system.

[0077] The top of the water separation tower 141 is connected in sequence to the condenser D142 and the reflux tank D143, and then returns to the top to form a circulation loop; the outlet of the reflux tank D143 is also connected to the condensate tank 114; methanol and tetrahydrofuran are separated at the top of the water separation tower 141, and after condensation, they are transported to the condensate tank 114 for repeated purification, and the bottom of the tower is water.

[0078] The top of the atmospheric pressure separation tower 151 is sequentially connected to a condenser E152 and a reflux tank E153, forming a circulation loop. The outlet of the reflux tank E153 is also connected to the feed inlet in the middle of the pressurized separation tower 161, preferably after preheating by the bottom heat exchanger 165 at the bottom of the pressurized separation tower 161 before being connected to the feed inlet in the middle of the pressurized separation tower 161. The tetrahydrofuran aqueous solution of a certain concentration obtained after extraction and separation in the extraction tower 131 enters the atmospheric pressure separation tower 151 for separation. The top yields an atmospheric pressure azeotrope of tetrahydrofuran and water, which, after condensation and preferably preheating by the bottom heat exchanger 165, enters the pressurized separation tower 161 for further separation. The bottom separation yields wastewater, which is collected.

[0079] The top of the pressurized separation tower 161 is connected in sequence to a condenser F162 and a reflux tank F163, and then returns to the top to form a circulation loop; the outlet of the reflux tank F163 is also connected to the middle of the atmospheric pressure separation tower 151; the atmospheric pressure azeotrope of tetrahydrofuran and water is separated in the pressurized separation tower 161, with tetrahydrofuran obtained at the bottom of the tower and a pressurized azeotrope of tetrahydrofuran and water separated at the top of the tower, which, after condensation, returns to the atmospheric pressure separation tower 151 for further distillation separation.

[0080] The bottom outlet of the pressurized separation tower 161 is connected to the external circulation reboiler 164, and then returns to the bottom to form a circulation loop. The bottom outlet of the pressurized separation tower 161 is also connected to the hot side of the bottom heat exchanger 165, after which tetrahydrofuran is discharged for collection. The outlet of the reflux tank E153, after passing through the cold side of the bottom heat exchanger 165, is connected to the feed inlet in the middle of the pressurized separation tower 161. The material in the reflux tank E153 exchanges heat with the material at the bottom of the pressurized separation tower 161 for preheating before entering the pressurized separation tower 161. More preferably, the external circulation reboiler 164 adopts a siphon heating method, and the heat medium is preferably steam at 0.1–3 MPa, but other heating media can also be used.

[0081] In this system, the material recycling tower 111 is a negative pressure distillation tower, and the pressurized separation tower 161 is a pressurized distillation tower.

[0082] use Figure 1 The method for separating transesterification vapors in the system specifically includes the following processes:

[0083] 1) The transesterification vapor generated in the transesterification reactor 101 enters the material recycling tower 111. The heavy components (dimethyl succinate, butanediol, and some oligomers) obtained at the bottom of the tower are returned to the transesterification reactor 101 for further reaction or discharged for collection as needed. Preferably, the heavy components (dimethyl succinate, butanediol, and some oligomers) obtained at the bottom of the material recycling tower 111 are collected by the material recycling pump 102, and after being diverted by the three-way valve 103, a portion is returned to the transesterification reactor 101 for further reaction under the control of the flow control valve 104, while the portion is collected. The gaseous components separated at the top of the tower (methanol, water, and light components such as tetrahydrofuran) are condensed and collected in the condensate tank 114, and then transported to the methanol recovery tower 121.

[0084] Preferably, the top temperature of the material recycling tower 111 is 85-105°C to ensure complete removal of low-boiling-point components; the bottom temperature is preferably 185-235°C; the operating pressure is preferably 0.6-1.3 bar (absolute pressure); and the reflux ratio is preferably 0.3-4.

[0085] Preferably, the heavy components obtained from the bottom of the material recycling tower 111 contain less than 0.1% methanol and water, with water content less than 800 ppm; this ensures that the recycled materials are reused without affecting the original transesterification reaction and guarantees the reaction material ratio for transesterification.

[0086] 2) After being processed by methanol recovery tower 121, the top vapor (mainly containing tetrahydrofuran, methanol and water) is condensed and enters the middle part of extraction tower 131. The bottom of the tower is purified to remove excess methanol and collected.

[0087] Preferably, the top temperature of the methanol recovery tower 121 is 55–65°C, the operating pressure is preferably atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is preferably 60–70°C, and the reflux ratio is preferably 0.5–20. Through this separation process, a purified mixture mainly composed of tetrahydrofuran, methanol, and water is obtained from the top of the tower.

[0088] Preferably, the methanol obtained at the bottom of the methanol recovery tower 121 has a purity greater than 98 wt%, which can ensure the effective recycling of methanol.

[0089] 3) Water is added from the top of the extraction tower 131 as an extractant to extract and distill the material entering the middle section. Methanol and extractant-water are obtained at the bottom of the tower and enter the water separation tower 141. Methanol and tetrahydrofuran are separated at the top of the water separation tower 141. After condensation, they are sent to the condensate tank 114 for repeated purification. The bottom of the tower is water, which is preferably returned to the top of the extraction tower 131 for recycling as an extractant.

[0090] Preferably, the top temperature of the extraction tower 131 is 55-70°C, the operating pressure is atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is 69-85°C, the reflux ratio is 0.5-30, and the ratio of the flow rate of the extractant water to the flow rate of the material entering the middle section is 3:1 to 1:2 to ensure effective separation of tetrahydrofuran and methanol.

[0091] Preferably, the top temperature of the water separation tower 141 is 55-70°C, the operating pressure is preferably atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is preferably 90-110°C, and the reflux ratio is preferably 1-5.

[0092] Preferably, the methanol content in the tetrahydrofuran aqueous solution obtained at the top of the extraction tower 131 is less than 0.1 wt%, which ensures the purity of the final tetrahydrofuran product in the subsequent tetrahydrofuran separation process.

[0093] Preferably, the water at the bottom of the water separation tower 141 has a purity greater than 99 wt% and can be returned to the extraction tower 131 as an extractant for reuse. The mixture of tetrahydrofuran and methanol with a water content of less than 1% is separated at the top of the tower and returned to the condensate tank 114 for recycling and purification, ensuring the effective utilization of materials.

[0094] 4) A tetrahydrofuran aqueous solution of a certain concentration is obtained from the top of the extraction tower 131 and enters the atmospheric pressure separation tower 151; the atmospheric pressure azeotrope of tetrahydrofuran and water is obtained from the top of the atmospheric pressure separation tower 151, and after condensation, it is first preheated by heat exchange with the bottom material of the pressurized separation tower 161, and then enters the pressurized separation tower 161, where wastewater is obtained from the bottom separation.

[0095] Preferably, the top temperature of the atmospheric pressure separation tower 151 is 55-70°C, the operating pressure is preferably atmospheric pressure to 1.2 bar (absolute pressure), the bottom temperature is preferably 90-110°C, and the reflux ratio is preferably 0.5-5.

[0096] 5) The atmospheric pressure azeotrope of tetrahydrofuran and water is separated in the pressure separation column 161. Qualified tetrahydrofuran (concentration greater than 99.5 wt%) is obtained at the bottom of the column, and the pressure azeotrope of tetrahydrofuran and water is separated at the top of the column. After condensation, it is returned to the atmospheric pressure separation column 151 for further distillation separation.

[0097] Tetrahydrofuran and water form an azeotrope. By pressure swing distillation, tetrahydrofuran and water can be effectively separated without introducing external extractants, and qualified tetrahydrofuran can be obtained at the same time.

[0098] Preferably, the top temperature of the pressurized separation tower 161 is 95–130°C, the operating pressure is 3–12 bar (absolute pressure), the bottom temperature is 110–140°C, and the reflux ratio is 1–15. Under these process conditions, the separation efficiency of tetrahydrofuran and aqueous solution through pressure swing separation is ensured, while keeping the manufacturing and operating costs of the equipment within a reasonable and scientific range.

[0099] like Figures 4-6 As shown, in the system of the present invention, the material recycling tower 111 includes a tower body 400. The top, sides, and bottom of the tower body 400 are respectively provided with a top gas phase outlet 402, a feed inlet 401, and a bottom liquid phase outlet 403. The tower body 400 is divided into a rectification section 404 located in the upper section and a stripping section 405 located in the lower section, with the feed inlet 401 as the boundary. The rectification section 404 is filled with structured packing 406; the stripping section 405 is provided with a plurality of large-aperture guide plates 407. The upper and lower sides of the notch edge of the large-aperture guide plates 407 are respectively provided with an overflow weir 409 and a downcomer 408.

[0100] Among them, such as Figure 6 As shown, the large-aperture guide plate 407 is provided with guide holes 411 and sieve holes 416. Figure 5As shown, a portion of the guide hole 411 extends obliquely upwards, protruding and covering at least a part of the guide hole 411, serving as a guide plate 410. An opening is formed between the guide plate 410 and the guide hole 411. This opening is parallel to the surface of the large-aperture guide plate 407, allowing the gaseous stream entering the guide hole 411 from below to change direction, ultimately aligning with the flow direction of the liquid phase on the large-aperture guide plate 407. The rising gaseous stream from the lower large-aperture guide plate 407 cuts and decomposes the liquid phase 412 near the guide hole 411 into multiple micro-units through the guide hole 411, facilitating mass transfer and improving the column's separation efficiency. The gas inlet and outlet ends of the guide hole 411 are designed with a certain curvature to reduce airflow resistance, increase mass transfer efficiency, and prevent the formation of dead zones on the plate, which could lead to oligomer deposition and blockage in the ester exchange liquid. The sieve holes 416 are used to allow the rising gas phase to pass through.

[0101] Preferably, the height of the overflow weir 409 is 5-45 mm; the radial section of the large-diameter guide tower plate 407 is an arc parallel to the side wall of the tower body, and the large-diameter guide tower plate 407 extends downward in a stepped manner with increasing arc diameter.

[0102] The central area of ​​the large-aperture guide plate 407 is designed with large-aperture sieve holes. Preferably, the sieve hole 416 has a diameter of 5 to 16 mm and an opening rate of 5 to 13%.

[0103] Preferably, the theoretical number of large-aperture guide trays 407 in the stripping section 405 accounts for 10% to 50% of the total number of trays, more preferably 20% to 40%.

[0104] The theoretical number of trays in the rectification section 404 accounts for 50% to 90% of the total number of trays, more preferably 60% to 80%.

[0105] The present invention will be further illustrated by specific embodiments below. Unless otherwise specified, the raw materials, equipment, and methods used in this invention are all commonly used in the art.

[0106] Example 1

[0107] use Figure 1 The transesterification vapor separation production line shown in the diagram is used to separate and purify the components in the transesterification process for preparing PBS.

[0108] 1) The transesterification vapor generated in the transesterification reactor 101 enters the material recovery tower 111. The heavy components obtained at the bottom of the tower (dimethyl succinate, butanediol, and some oligomers) are returned to the transesterification reactor 101 for further reaction. The gaseous components separated at the top of the tower are condensed and collected in the condensate tank 114, and then sent to the methanol recovery tower 121. The top temperature of the material recovery tower 111 is 73℃, the bottom temperature is 225℃, the operating pressure is 1 bar (absolute pressure), and the reflux ratio is 0.3. The methanol content in the bottom recovery material separated by the material recovery tower 111 is less than 0.1 wt%, and the water content is 500 ppm.

[0109] 2) After treatment in methanol recovery tower 121, the overhead vapor mainly contains tetrahydrofuran, methanol, and water. After condensation, it enters the middle section of extraction tower 131. The methanol recovery tower 121 has a top temperature of 60°C, an operating pressure of 1 bar (absolute pressure), a reflux ratio of 10, and a bottom temperature of 65°C. Through the above separation process, a purified mixture mainly composed of tetrahydrofuran, methanol, and water is simultaneously separated at the top. After treatment in the methanol removal tower, the methanol obtained at the bottom has a purity greater than 98 wt%, ensuring effective methanol recycling.

[0110] 3) Water is used as the extractant and added from the top of extraction tower 131. The material entering the middle section undergoes extractive distillation, with methanol and extractant-water as the main components at the bottom. This mixture then enters water separation tower 141. At the top of water separation tower 141, methanol and tetrahydrofuran solution (water content less than 1%) are separated and condensed, then sent to condensate tank 114 for repeated purification. The water obtained at the bottom is returned to the top of extraction tower 131 for reuse as the extractant. A certain concentration of tetrahydrofuran and an aqueous solution are separated at the top of extraction tower 131 and enter atmospheric pressure separation tower 151. The top temperature of extraction tower 131 is 63℃, the absolute operating pressure is atmospheric pressure, the reflux ratio is 7, the bottom temperature is 75℃, and the flow rate ratio of extractant water to material is 1:2. The bottom stream of extraction column 131 enters water separation column 141 for methanol separation and water reuse. The top temperature of water separation column 141 is 60℃, the absolute operating pressure is atmospheric pressure, the reflux ratio of the column is 2, and the bottom temperature is 100℃.

[0111] 4) The tetrahydrofuran aqueous solution of a certain concentration obtained after extraction and separation enters the atmospheric pressure separation tower 151. Wastewater is separated at the bottom and collected. An atmospheric pressure azeotrope of tetrahydrofuran and water is obtained at the top. After being heated by the bottom heat exchanger 165, it enters the pressurized separation tower 161. The top temperature of the atmospheric pressure separation tower is 65℃, the absolute operating pressure is atmospheric pressure, the reflux ratio is 2, and the bottom temperature is 100℃. The atmospheric pressure azeotrope of water and tetrahydrofuran is obtained at the top of the atmospheric pressure separation tower 151. After being preheated by the bottom heat exchanger 165, the atmospheric pressure azeotrope enters the pressurized separation tower 161. The concentration of water separated at the bottom is greater than 99.5 wt%.

[0112] 5) The atmospheric pressure azeotrope of tetrahydrofuran and water is separated in pressure separation column 161. The absolute operating pressure is 5 bar, the reflux ratio of the column is 1.5, and the bottom temperature of the column is 126°C. Tetrahydrofuran with a purity greater than 99.5% is obtained from the bottom of the column. After condensation, it is collected. The pressure azeotrope of tetrahydrofuran and water is separated from the top. After condensation, it is returned to atmospheric pressure separation column 151 for further distillation separation.

[0113] The material recycling tower 111 is specifically adopted as follows: Figures 4-6 The tower structure is shown. The theoretical number of trays in the large-aperture guide plate 407 accounts for 30% of the total number of trays, and the theoretical number of trays in the rectification section 404 accounts for 70% of the total number of trays. The central area of ​​the large-aperture guide plate 407 has large-aperture sieve holes 416 with an opening diameter of 13 mm and an opening ratio of 12%. Overflow weirs 409 and downcomers 408 are respectively provided on the upper and lower sides of the notch edge of the large-aperture guide plate 407. The overflow weir 409 has a height of 15 mm. The radial cross-section of the large-aperture guide plate 407 is an arc shape parallel to the side wall of the tower body, and the downcomer guide plate extends downwards in a stepped manner with increasing arc diameter.

[0114] Taking a PBS production facility with a capacity of 10,000 tons / year and a flow rate of 12,500 kg / hr as an example, using transesterification vapor to produce PBS, the process is as follows: Figure 1 The process flow ultimately separates tetrahydrofuran with a purity exceeding 99.8% and methanol with a purity of 98.5% from the refining tower. Furthermore, all reactants, methanol, and tetrahydrofuran are separated and collected to the maximum extent possible. Additionally, the process utilizes the heat source at the bottom of the pressurized separation tower 161 to reheat the feed material entering the tower; the water separated in the water separation tower 141 is returned as extractant for secondary use; and the material separated at the top of the tower is recycled for refining. This process improves product recovery rate and achieves energy saving and consumption reduction.

[0115] Comparative Example 1

[0116] use Figure 2The separation and purification production line for the transesterification solution used in the preparation of PBS via transesterification shown in the example separates and purifies each component. The relevant process parameters for processes 1)-3) are consistent with those in Example 1. The difference lies in the reversed order of atmospheric pressure separation tower 151 and pressurized separation tower 161; that is, tetrahydrofuran is first separated under pressure, followed by tetrahydrofuran separation at atmospheric pressure. Specifically, as follows:

[0117] The tetrahydrofuran aqueous solution of a certain concentration obtained after extraction and separation is fed into a pressurized separation column 161 for separation. The operating pressure is 5 bar, the reflux ratio of the column is 5, the top temperature is 115°C, and the bottom temperature is 125°C. Tetrahydrofuran with a purity greater than 99.5% is obtained at the bottom of the column and collected after condensation. The pressurized azeotrope of tetrahydrofuran and water is separated at the top and, after condensation, enters an atmospheric pressure separation column 151 for distillation separation.

[0118] The pressurized azeotrope of tetrahydrofuran and water enters the atmospheric pressure separation column 151. Wastewater is separated at the bottom and collected, while the atmospheric pressure azeotrope of tetrahydrofuran and water at the top is sent to the pressurized separation column 161. The atmospheric pressure separation column 151 has a top temperature of 65°C, an absolute operating pressure of atmospheric pressure, a reflux ratio of 2, and a bottom temperature of 100°C. The atmospheric pressure azeotrope of water and tetrahydrofuran obtained at the top of the atmospheric pressure separation column 151 is condensed and then enters the pressurized separation column 161. The water concentration separated at the bottom of the column is greater than 99.5 wt%.

[0119] pass Figure 2 The process flow can ultimately separate methanol with a purity of over 98.5% and tetrahydrofuran with a purity of 99.8 wt% from the refining tower system. However, because the final product tetrahydrofuran is extracted in the middle of the system, the system is less stable under unstable operating conditions than when tetrahydrofuran is extracted at the end. Furthermore, the material undergoes pressure separation of tetrahydrofuran first, which leads to a significant increase in the throughput of the tetrahydrofuran pressure separation tower and an increase in the tower's manufacturing cost.

[0120] Comparative Example 2

[0121] use Figure 3 The ester exchange vapor separation production line for PBS preparation shown in the diagram separates and purifies the various components. Process 1) has the same process parameters as in Example 1, except that the methanol recovery tower 121 is omitted. After the ester exchange vapor is separated by the material recycling tower 111, the top product directly enters the extraction tower 131 for extraction separation. Details are as follows:

[0122] Water is added from the top of extraction tower 131 as the extractant, and undergoes extractive distillation with the material entering the middle section. Methanol and extractant-water are obtained at the bottom, and then enter water separation tower 141. Methanol is separated at the top of water separation tower 141, and after condensation, part of it is refluxed and part is collected. The water obtained at the bottom is returned to the top of extraction tower 131 for reuse as the extractant. A certain concentration of tetrahydrofuran and an aqueous solution are separated at the top of extraction tower 131 and enter tetrahydrofuran atmospheric pressure separation tower 151. The top temperature of extraction tower 131 is 64℃, the absolute operating pressure is atmospheric pressure, the reflux ratio is 6, the bottom temperature is 76℃, and the flow rate ratio of extractant water to material is 1:1. The bottom stream of extraction tower 131 enters water separation tower 141 for methanol separation and water reuse. The top temperature of water separation tower 141 is 64℃, the absolute operating pressure is atmospheric pressure, the reflux ratio is 3, and the bottom temperature is 100℃.

[0123] After separation in extraction tower 131, the methanol content at the top of extraction tower 131 is 0.2 wt%. The liquid separated at the bottom of extraction tower 131 enters water separation tower 141. The water purity at the bottom of water separation tower 141 is greater than 98 wt%. 99% methanol is separated at the top of the tower and collected.

[0124] pass Figure 3 The process flow can ultimately separate 1,3-propanediol with a purity of over 99% and tetrahydrofuran with a purity of 99.8% from the refining tower system. However, because the transesterification vapor contains a large amount of methanol after passing through the material recovery tower, directly using water for extractive distillation will lead to an increase in the amount of extractant-water, resulting in the loss of methanol and tetrahydrofuran. Furthermore, after the bottom material of the extraction tower is separated by the water separation tower, the water contains other heavy components and cannot be directly reused, consuming a large amount of water.

[0125] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A separation system for transesterification vapor in the preparation of PBS by transesterification, wherein, The separation system includes: an ester exchange reactor (101), a material recycling tower (111), a methanol recovery tower (121), an extraction tower (131), a water separation tower (141), an atmospheric pressure separation tower (151), and a pressurized separation tower (161). The top of the ester exchange reactor (101) is connected to the feed inlet in the middle of the material recycling tower (111), and the bottom of the material recycling tower (111) is connected to the top of the ester exchange reactor (101). The top of the material recycling tower (111) is connected in sequence to condenser A (112) and reflux tank A (113), and then returns to the top to form a circulation loop; the outlet of the reflux tank A (113) is also connected to condensate tank (114), and the outlet of the condensate tank (114) is connected to the feed inlet in the middle of the methanol recovery tower (121). The top of the methanol recovery tower (121) is connected in sequence to the condenser B (122) and the reflux tank B (123), and then returns to the top to form a circulation loop; the outlet of the reflux tank B (123) is also connected to the feed inlet in the middle of the extraction tower (131). The top of the extraction tower (131) is connected in sequence to the condenser C (132) and the reflux tank C (133), and then returns to the top to form a circulation loop. The outlet of the reflux tank C (133) is also connected to the feed inlet in the middle of the atmospheric pressure separation tower (151). The upper part of the extraction tower (131) is provided with a water inlet, and the bottom is connected to the feed inlet in the middle of the water separation tower (141). The top of the water separation tower (141) is connected in sequence to the condenser D (142) and the reflux tank D (143), and then returns to the top to form a circulation loop; the outlet of the reflux tank D (143) is also connected to the condensate tank (114). The top of the atmospheric pressure separation tower (151) is connected in sequence to the condenser E (152) and the reflux tank E (153), and then returns to the top to form a circulation loop; the outlet of the reflux tank E (153) is also connected to the feed inlet in the middle of the pressurized separation tower (161). The top of the pressurized separation tower (161) is connected in sequence to the condenser F (162) and the reflux tank F (163), and then returns to the top to form a circulation loop; the outlet of the reflux tank F (163) is also connected to the middle of the atmospheric pressure separation tower (151).

2. The separation system according to claim 1, wherein, The bottom of the water separation tower (141) is connected to the water inlet at the top of the extraction tower (131).

3. The separation system according to claim 1, wherein, The bottom of the material recycling tower (111), methanol recovery tower (121), extraction tower (131), water separation tower (141) and atmospheric pressure separation tower (151) are all equipped with reboilers.

4. The separation system according to claim 1, wherein, The bottom outlet of the pressurized separation tower (161) is connected to the external circulation reboiler (164) and then returns to the bottom to form a circulation loop; the bottom outlet of the pressurized separation tower (161) is also connected to the hot side of the bottom heat exchanger (165), and then outputs tetrahydrofuran material for collection; the outlet of the reflux tank E (153) is connected to the feed inlet in the middle of the pressurized separation tower (161) after passing through the cold side of the bottom heat exchanger (165).

5. The separation system according to claim 1, wherein, The pipeline connecting the bottom of the material recycling tower (111) to the top of the ester exchange reactor (101) is equipped with a material recycling pump (102), a three-way valve (103) and a flow control valve (104) in sequence.

6. The separation system according to claim 1, wherein, The material recycling tower (111) includes a tower body (400), which includes a rectification section (404) in the upper section and a stripping section (405) in the lower section. The rectification section (404) is filled with structured packing (406); the stripping section (405) is provided with several large-aperture guide plates (407), the large-aperture guide plates (407) are provided with guide holes (411) and sieve holes (416), part of the edge of the guide hole (411) extends obliquely upward to cover at least part of the guide hole (411) as a guide plate (410), and a slit opening is formed between the guide plate (410) and the guide hole (411), the slit opening is parallel to the surface of the large-aperture guide plate (407) on which it is located; the sieve hole (416) has a pore diameter of 5~16mm and an opening rate of 5~13%.

7. The separation system according to claim 6, wherein, The large-aperture guide plate (407) has an overflow weir (409) and a downcomer (408) on the upper and lower sides of the notch edge, respectively.

8. The separation system according to claim 6, wherein, The theoretical number of large-aperture guide trays (407) in the stripping section (405) accounts for 10% to 50% of the total number of trays; The theoretical number of plates in the rectification section (404) accounts for 50% to 90% of the total number of plates.

9. A method for separating transesterification vapor in the preparation of PBS by transesterification, wherein, The separation method is performed using the separation system described in any one of claims 1-8; The separation method Includes the following processes: The transesterification vapor generated in the transesterification reactor (101) enters the material recycling tower (111). The heavy components obtained at the bottom of the tower are returned to the transesterification reactor (101) for further reaction or discharged and collected as needed. The gas phase components separated at the top of the tower are condensed and collected in the condensate tank (114), and then transported to the methanol recovery tower (121). After being processed by the methanol recovery tower (121), the top vapor of the tower is condensed and enters the middle part of the extraction tower (131), and the bottom of the tower is purified to remove excess methanol and collected. Water is added from the top of the extraction tower (131) as an extractant to extract and distill the material entering the middle section. Methanol and extractant-water are obtained at the bottom of the tower and enter the water separation tower (141). Methanol and tetrahydrofuran are separated at the top of the water separation tower (141), and after condensation, they are sent to the condensate tank (114) for repeated purification. Water is obtained at the bottom of the tower. A tetrahydrofuran aqueous solution of a certain concentration is obtained at the top of the extraction tower (131) and enters the atmospheric pressure separation tower (151). An atmospheric pressure azeotrope of tetrahydrofuran and water is obtained at the top of the atmospheric pressure separation tower (151), and after condensation, it enters the pressurized separation tower (161). Wastewater is obtained at the bottom of the tower. The atmospheric pressure azeotrope of tetrahydrofuran and water is separated in a pressure separation column (161). Tetrahydrofuran is obtained at the bottom of the column, and the pressure azeotrope of tetrahydrofuran and water is separated at the top of the column. After condensation, it is returned to the atmospheric pressure separation column (151) for further distillation separation.

10. The separation method according to claim 9, wherein, The water at the bottom of the water separation tower (141) is returned to the upper part of the extraction tower (131) for recycling as an extractant.

11. The separation method according to claim 9, wherein, The atmospheric azeotrope of tetrahydrofuran and water obtained at the top of the atmospheric separation tower (151) is condensed and preheated by exchanging heat with the bottom material of the pressurized separation tower (161) before entering the pressurized separation tower (161).

12. The separation method according to claim 9, wherein, The heavy components obtained at the bottom of the material recycling tower (111) are collected by the material recycling pump (102). After being diverted by the three-way valve (103), part of the components are returned to the ester exchange reactor (101) for further reaction under the control of the flow control valve (104), and the rest are collected.

13. The separation method according to claim 9, wherein, The material recycling tower (111) has a top temperature of 85~105℃, a bottom temperature of 185~235℃, an operating pressure of 0.6~1.3 bar absolute pressure, and a reflux ratio of 0.3~4.

14. The separation method according to claim 9, wherein, The methanol recovery tower (121) has a top temperature of 55~65℃, an operating pressure of atmospheric pressure to absolute pressure of 1.2 bar, a bottom temperature of 60~70℃, and a reflux ratio of 0.5~20.

15. The separation method according to claim 9, wherein, The extraction tower (131) has a top temperature of 55~70℃, an operating pressure of atmospheric pressure to absolute pressure of 1.2 bar, a bottom temperature of 69~85℃, a reflux ratio of 0.5~30, and a ratio of the flow rate of the extractant water to the flow rate of the material entering the middle section of 3:1 to 1:

2.

16. The separation method according to claim 9, wherein, The water separation tower (141) has a top temperature of 55~70℃, an operating pressure of atmospheric pressure to absolute pressure of 1.2 bar, a bottom temperature of 90~110℃, and a reflux ratio of 1~5.

17. The separation method according to claim 9, wherein, The atmospheric pressure separation column (151) has a top temperature of 55~70℃, an operating pressure of atmospheric pressure to absolute pressure of 1.2 bar, a bottom temperature of 90~110℃, and a reflux ratio of 0.5~5.

18. The separation method according to claim 9, wherein, The pressurized separation tower (161) has a top temperature of 95~130℃, an operating pressure of 3~12 bar absolute pressure, a bottom temperature of 110~140℃, and a reflux ratio of 1~15.

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