A system and method for the production of tetrahydrofuran from 1,4-butanediol

Abstract

The application discloses a system and method for preparing tetrahydrofuran from 1,4-butanediol. The application proposes a new process for preparing THF by adopting fixed bed solid acid catalysis under low-temperature full liquid phase condition, and combining liquid membrane dehydration. The reaction adopts solid acid low-temperature catalysis cyclization reaction, the THF selectivity can reach more than 99.5%, no n-butyl aldehyde and isobutyl aldehyde impurities are generated, and the equipment corrosion problem caused by the traditional sulfuric acid method is solved. The product 20% water and 80% THF directly enters the liquid membrane dehydration assembly in liquid phase, the water content can be reduced to below 1%, and then THF with water content below 100ppm can be obtained through simple separation dehydration under normal pressure. The total BDO conversion rate of the reaction reaches 100%, the THF selectivity is more than 99.5%, the product purity is greater than 99.9%, and the water content is below 100ppm.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and specifically to a system and method for preparing tetrahydrofuran from 1,4-butanediol. Background Technology

[0002] Tetrahydrofuran (THF) is an important organic chemical raw material widely used in pharmaceuticals, chemicals, electronics, and other fields. Its most important application is in the production of polytetramethylene ether glycol (PTMEG), with downstream applications in spandex production. The dehydration and cyclization of 1,4-butanediol (BDO) is the primary method for preparing THF.

[0003] Currently, industrial-scale THF production uses BDO synthesized under sulfuric acid catalyst, which presents problems such as equipment corrosion, numerous side reactions, and complex processes. Large amounts of BDO and THF tar remain in the reactor bottoms, requiring regular daily venting, resulting in material waste and poor atom economy.

[0004] Furthermore, THF applications have stringent requirements regarding moisture content, and the market has a large demand for anhydrous THF with high quality requirements. Currently, THF separation and dehydration processes all employ three-tower distillation, but because THF and water form an azeotropic reaction, low- and high-pressure distillation consumes a lot of energy. Some research institutions have proposed using pervaporation membrane dehydration, but the multiple vaporization and liquefaction of the material increases the steam and cooling water load during the separation process, resulting in high energy consumption. Moreover, the membrane operates at high temperatures, experiences excessive loads, and has a short lifespan, leading to high production costs.

[0005] To address the issues of corrosion and numerous byproducts associated with the sulfuric acid process, SU1158562A1 discloses a method for preparing tetrahydrofuran (THF) using γ-alumina or chlorine-containing γ-alumina as a catalyst at 320°C and atmospheric pressure. When the conversion rate of 1,4-butanediol is 100%, both the conversion rate and selectivity decrease to below 95% with increasing throughput, indicating limited alumina throughput. CN211394335U discloses a reactive distillation method where the catalyst is in the bottom of a column, and gas stirring replaces mechanical stirring to alleviate catalyst breakage. A two-stage nanofiltration process improves the purity of THF. However, this process still suffers from catalyst pulverization, and the condensation of the top steam before nanofiltration results in multiple cooling and heating cycles for both THF and water, leading to high energy consumption.

[0006] Regarding the separation of THF and water, it is well known in the art that THF and water form an azeotrope under normal pressure, with a composition of approximately 95 wt% THF and 5 wt% water; under 0.6 MPaG conditions, the azeotrope composition is approximately 89 wt% THF and 11 wt% water. Utilizing this property, a three-tower distillation process involving a low-pressure tower, a high-pressure tower, and a refining tower is widely used to separate THF and water. First, the THF stream enters the low-pressure tower, and a low-water-content THF stream is collected from the top. This stream then enters the high-pressure tower. Due to the increased pressure within the high-pressure tower and the aforementioned characteristics of the THF-water azeotrope, the water content in the stream collected from the top of the high-pressure tower increases, while the water content in the stream collected from the bottom of the high-pressure tower decreases. Therefore, the stream from the bottom of the high-pressure tower enters the refining tower for further purification, ultimately yielding high-purity THF; while the THF stream with increased water content collected from the top of the high-pressure tower is recycled back to the feed inlet of the low-pressure tower. During this process, a large amount of tetrahydrofuran aqueous solution continuously circulates between the low-pressure tower and the high-pressure tower, causing the low-pressure tower and the high-pressure tower to operate at high loads continuously, thereby consuming a large amount of heating steam and cooling water.

[0007] CN114031580A proposes a low-energy-consumption tetrahydrofuran (THF) refining device and method. By organically combining zeolite membrane dehydration with three-tower distillation and employing a pervaporation membrane separation process, energy consumption can be significantly reduced. However, since THF and water still need to be vaporized and separated in gaseous form, energy consumption remains high. CN115554721A proposes a tetrahydrofuran refining device and method with integrated tower and membrane dehydration. The aqueous tetrahydrofuran feed solution is preheated and fed into the first distillation tower. The top of the first distillation tower can be directly fed into the membrane dehydration unit in gaseous phase. The dehydrated tetrahydrofuran can be collected in gaseous phase and condensed in the reboiler at the bottom of the second distillation tower. The top of the second distillation tower can also be collected in gaseous phase and condensed in the reboiler at the bottom of the third distillation tower. This process uses a pervaporation membrane dehydration combined with a three-tower process, resulting in large equipment investment, high separation pressure, and the potential for side reactions and material loss due to the high-temperature heat-sensitive substance THF. Furthermore, the material still requires vaporization. CN106543112A proposes a process using membrane separation coupled with pressure swing distillation to reduce the amount of tetrahydrofuran circulating. However, the process still requires passing through reactors, atmospheric distillation columns, and high-pressure distillation columns, and there are problems such as incomplete BDO conversion during the dehydration reaction process and large heavy oil emissions.

[0008] Therefore, there is an urgent need for a production technology for preparing tetrahydrofuran from BDO that is highly efficient in reaction, has high atom utilization, high separation and dehydration efficiency, and low cost, which would be conducive to achieving green and low-energy production of tetrahydrofuran. Summary of the Invention

[0009] The purpose of this invention is to provide a system and method for preparing tetrahydrofuran from 1,4-butanediol.

[0010] This invention combines fixed-bed solid acid cyclization reaction, liquid-phase membrane separation, and extractive distillation or atmospheric distillation processes. Calculations show that the water content at the liquid-phase membrane separation outlet is reduced to about 0.5-1%, with the lowest membrane investment and energy consumption.

[0011] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a system for preparing tetrahydrofuran from 1,4-butanediol (BDO), the system comprising: Fixed-bed reactor: Its catalyst bed is filled with solid acid catalyst, and the bottom feed port is used to feed 1,4-butanediol (BDO) for cyclization and dehydration reaction to produce tetrahydrofuran (BDO single-pass conversion rate is 50%~99.5%). The top outlet is equipped with a back pressure valve to control the pressure inside the fixed-bed reactor so that all materials in the reactor are in the liquid phase. Liquid phase membrane dehydration component: Its inlet is connected to the top outlet of the fixed bed reactor, and the quaternary side outlet yields THF material with a water content of less than 1%; BDO Recovery Tower: The osmotic side outlet of the liquid phase membrane dehydration component is connected to the bottom inlet of the BDO recovery tower; the BDO recovery tower uses 1,4-butanediol to enter from the top of the tower for extractive distillation to remove residual water from the material, and the top outlet of the tower yields a qualified dehydrated THF stream (water content less than 100 ppm), and the BDO material obtained from the bottom of the tower is recycled back to the fixed bed reactor for further reaction; Hydrogenation reactor: Its bottom inlet is connected to the top outlet of the BDO recovery tower. Unsaturated substances (such as dihydrofuran) in the material undergo hydrogenation reaction, and THF material with an unsaturated substance (dihydrofuran) content of less than 2 ppm is obtained from the top outlet. Heavy removal tower: Its bottom inlet is connected to the top outlet of the hydrogenation reactor, and the top outlet of the tower produces polymer-grade THF product (purity greater than 99.9%, water content less than 100 ppm, and dihydrofuran less than 2 ppm). A small amount of waste oil is discharged from the bottom of the tower.

[0012] According to the system of the present invention, preferably, the fixed bed reactor is a radial fixed bed reactor, wherein the catalyst bed is coaxially and annularly packed with the reactor, and a liquid distributor is provided at the middle position in the axial direction.

[0013] Traditional fixed-bed reactors are typically stacked-bed reactors, with reactants entering from the bottom and exiting from the top, or vice versa. The resin bed at the reactor inlet is subject to significant impact from the liquid phase and the reactants, leading to catalyst pulverization, high bed pressure drop, or blockage. This is especially true for the catalyst particles used in this invention, which have a diameter of less than 0.2-1 mm, making bed blockage even more likely. Therefore, the fixed-bed reactor of this invention is specially designed for more uniform material distribution. BDO feedstock enters the intermediate liquid distributor from the bottom of the annularly packed reactor. Under the action of the distributor, the BDO feedstock uniformly passes radially (laterally) through the catalyst bed for reaction, then collects at the top of the reactor and exits as a liquid phase after being back-pressurized by a back-pressure valve. This reactor significantly reduces bed pressure drop, ensuring optimal reaction efficiency for the cyclization of BDO to THF.

[0014] According to the system obtained by the present invention, preferably, the set temperature inside the fixed bed reactor is 80~140℃.

[0015] According to the system obtained by the present invention, preferably, the solid acid catalyst is a strong acid cation exchange resin catalyst.

[0016] In the above scheme, the BDO recovery tower uses the system's own raw material BDO as the extractant. While recovering BDO, a small amount of anhydrous BDO is added for extractive distillation to further remove the less than 1% water remaining in the THF after dehydration of the liquid phase membrane, reducing the product water content to below 100 ppm. There is no need to add a new separation tower to separate the remaining less than 1% water, reducing equipment investment. Moreover, compared with the traditional extractive distillation process, no new extractant is added, avoiding the separation and recovery of the extractant.

[0017] In another specific embodiment of the present invention, the 1,4-butanediol (BDO) feed at the top of the BDO recovery tower is eliminated, and an atmospheric dehydration tower is provided in the system after the BDO recovery tower and before the hydrogenation reactor; The top outlet of the BDO recovery tower is connected to the bottom inlet of the atmospheric dehydration tower, the bottom outlet of the atmospheric dehydration tower is connected to the bottom inlet of the hydrogenation reactor, and the top outlet is connected to the inlet of the liquid membrane dehydration assembly. THF with approximately 5% water content is returned to the inlet of the liquid membrane dehydration assembly at the top of the tower.

[0018] In this scheme, a new atmospheric dehydration tower replaces BDO extraction for dehydration, effectively removing water content to below 100 ppm. The atmospheric dehydration tower is combined with a liquid-phase membrane separation unit. Membrane separation easily reduces water content from 20% to below 1%, requiring a small membrane area and minimal investment. By combining membrane separation with atmospheric separation, water content can be reduced from 20% to 100 ppm while minimizing overall equipment investment. Furthermore, compared to conventional high- and low-pressure distillation, atmospheric separation results in lower system pressure and operating temperature, reducing THF polymerization losses at high temperatures and increasing overall product yield.

[0019] Preferably, the set temperature of the atmospheric pressure dehydration tower is 67~90℃.

[0020] In another specific embodiment of the present invention, the BDO recovery tower is disposed before the liquid phase membrane dehydration assembly; The top outlet of the fixed-bed reactor is connected to the bottom inlet of the BDO recovery tower, the top outlet of the BDO recovery tower is connected to the inlet of the liquid membrane dehydration assembly, and the osmosis side outlet of the liquid membrane dehydration assembly is connected to the bottom inlet of the atmospheric pressure dehydration tower.

[0021] In this scheme, unreacted BDO is first recovered, followed by liquid-phase membrane dehydration. The cyclic reaction is separated from the THF separation, making the fixed-bed cyclization reaction operation more flexible. The main difference between the two schemes—before and after the liquid-phase membrane dehydration unit—lies in the different membrane performance requirements. The latter requires a membrane with higher acid resistance, while the former has slightly lower requirements.

[0022] According to the system obtained by the present invention, preferably, the temperature inside the fixed-bed reactor is set at 80~140℃. A back pressure valve is provided at the top outlet of the fixed-bed reactor to control the pressure inside the reactor, while the reaction temperature is controlled at 80~140℃. Through the dual conditions of the back pressure valve and the reaction temperature, it is ensured that the cyclization products water and THF are both in the liquid phase.

[0023] According to the system obtained by the present invention, for the liquid phase membrane dehydration component, since it is a full liquid phase feed, the liquid phase membrane used needs to have strong water resistance and a certain degree of acid resistance; preferably, a CHA separation membrane or a NaA type molecular sieve membrane is used. More specifically, for the scheme of performing membrane dehydration first and then BDO recovery and extraction (i.e., the BDO recovery tower is after the liquid phase membrane dehydration component), all reactants need to enter the liquid phase membrane dehydration component. Since the materials contain a small amount of acidic impurities, the membrane needs to have high acid resistance, and a CHA separation membrane is preferred; for the scheme of performing BDO recovery first (i.e., the BDO recovery tower is before the liquid phase membrane dehydration component), the acidic impurities are separated by the BDO recovery tower, and the top effluent of the tower is almost free of acidic impurities. The requirements for the membrane are slightly lower, and a cheaper NaA molecular sieve membrane can be used.

[0024] Another aspect of the present invention provides a method for preparing tetrahydrofuran from 1,4-butanediol, which is carried out by any of the above systems and includes the following processes: 1,4-Butanediol enters a fixed-bed reactor for cyclization and dehydration to produce tetrahydrofuran. The single-pass conversion rate of BDO is 50%~99.5%, and the specific conversion rate increases with increasing temperature. The top discharge of the fixed bed reactor enters the liquid phase membrane dehydration component in liquid phase form for liquid phase membrane dehydration. The permeate side yields THF material with a water content of less than 1%, while the permeate side discharges wastewater. The effluent from the osmotic side of the liquid membrane dehydration unit is sent to the BDO recovery tower to recover 1,4-butanediol and remove residual water. The 1,4-butanediol material obtained in the bottom of the tower is recycled back to the fixed-bed reactor for further reaction. THF stream with qualified dehydration (water content less than 100 ppm) is obtained at the top outlet of the tower. The dehydrated THF stream is sent to the hydrogenation reactor to hydrogenate the small amount of unsaturated substances in the THF. The top outlet yields THF material with an unsaturated substance (dihydrofuran) content of less than 2 ppm. It then enters the de-heavy column, and the top outlet yields polymer-grade THF product (purity greater than 99.9%, water content less than 100 ppm, and dihydrofuran content less than 2 ppm). A small amount of waste oil is discharged from the bottom of the column.

[0025] According to the method of the present invention, preferably, the reaction temperature in the fixed-bed reactor is 80~140℃, more preferably 90~135℃, and more preferably 100~125℃; the pressure is 0.2~1 MPaG, more preferably 0.2~0.7 MPaG, and more preferably 0.4~0.6 MPaG.

[0026] According to the method of the present invention, preferably, the reaction space velocity of the fixed-bed reactor is 0.5~4 h⁻¹. -1 Preferably 0.5~3 h-1 More preferably 0.5~2 h -1 .

[0027] According to the method of the present invention, preferably, the temperature of the liquid phase membrane dehydration is 40~120℃, more preferably 50~110℃, and even more preferably 60~100℃; the pressure is 0~0.4 MPaG, more preferably 0.1~0.3 MPaG.

[0028] According to the method of the present invention, preferably, the feed water content of the liquid phase membrane dehydration component is 5% to 30%, more preferably 10% to 20%; and the discharge water content is 0.1% to 1%, more preferably 0.2% to 1%, and more preferably 0.2% to 0.5%.

[0029] According to the method of the present invention, preferably, the reflux ratio of the BDO recovery tower is 0.2~4, more preferably 0.5~2; the operating pressure is 0~0.2 MPaG, and the bottom temperature is 67~160℃; the amount of 1,4-butanediol entering from the top of the tower is 0.1~1 times the feed mass, more preferably 0.1~0.5 times; and the concentration of the 1,4-butanediol material obtained from the bottom of the tower is 70~99%, more preferably 90~99%.

[0030] According to the method of the present invention, preferably, the catalyst for the hydrogenation reaction is a Cu-based or Ni-based catalyst, the reaction temperature is 50-110°C, the pressure is 0.5-1 MPaG, and the reaction space velocity is 0.5-4 h⁻¹. -1 More preferably 0.5~2 h -1 .

[0031] According to the method of the present invention, preferably, the reflux ratio of the deweighting tower is 0.5~5, the operating pressure is 0~0.2MPaG, and the tower bottom temperature is 67~100℃.

[0032] In another specific implementation, the method eliminates the feeding of 1,4-butanediol from the top of the BDO recovery tower, and after BDO recovery, the material obtained from the top outlet of the BDO recovery tower is sent to an atmospheric dehydration tower for atmospheric dehydration to remove residual water; then it enters the subsequent hydrogenation reactor and deweighting tower.

[0033] Preferably, the temperature for atmospheric pressure dehydration is 67~90℃.

[0034] In another specific implementation, the method first performs BDO recovery, followed by liquid-phase membrane dehydration. In this approach, unreacted BDO is recovered first, and then liquid-phase membrane dehydration is performed, separating the cyclic reaction from THF separation, making the fixed-bed cyclization reaction operation more flexible.

[0035] This invention proposes a novel process for preparing THF using a fixed-bed solid acid catalysis reaction under low-temperature, all-liquid-phase conditions, combined with liquid-phase membrane dehydration to produce tetrahydrofuran. The reaction employs a low-temperature solid acid catalytic cyclization reaction, achieving a THF selectivity of over 99.5%, with no n-butyraldehyde or isobutyraldehyde impurities generated, thus solving the equipment corrosion problems associated with the traditional sulfuric acid process. The product, consisting of 20% water and 80% THF, is directly fed into a liquid-phase membrane dehydration unit, reducing the water content to below 1%. Subsequent simple separation and dehydration under atmospheric pressure yields THF with a water content below 100 ppm. This invention achieves a 100% total BDO conversion rate, a THF selectivity exceeding 99.5%, a product purity greater than 99.9%, and a water content below 100 ppm.

[0036] The system and method provided by this invention achieve continuous green production of tetrahydrofuran from 1,4-butanediol. A fixed-bed cyclization reaction combined with BDO recovery achieves 100% BDO conversion and THF selectivity exceeding 99.5%. Liquid-phase membrane dehydration combined with extractive distillation or atmospheric distillation to separate byproduct water significantly reduces energy consumption in THF purification and separation. The product purity is above 99.9%, with water content below 100 ppm and dihydrofuran below 2 ppm. The process is green, with low investment and operating costs and high product yield.

[0037] In addition, compared with the prior art, the present invention has the following beneficial effects: 1) Solid acid catalysis replaces the traditional sulfuric acid process, resulting in less equipment corrosion, no need for special reactor materials, and a simpler process.

[0038] 2) A fixed-bed reactor is used for the whole liquid phase reaction, which minimizes wear on the solid acid catalyst. The single-pass conversion rate of BDO is 50%~70%. The conversion rate is controlled at an appropriate level, and no n-butyraldehyde or isobutyraldehyde impurities are generated. The THF selectivity is as high as 99.5% or more, and the amount of total tar and other by-products discharged is greatly reduced, resulting in high atom economy.

[0039] 3) Liquid-phase membrane dehydration is used instead of traditional three-tower distillation or pervaporation membrane separation processes. First, a liquid-phase membrane separation unit is used to reduce the water content of THF to below 1%, which minimizes investment and energy consumption. Then, BDO extractive distillation is used to remove the remaining 0.5% water, or atmospheric pressure distillation is used to obtain almost water-free THF. This reduces the number of water removal towers by two, resulting in lower equipment investment. Simultaneously, liquid-phase dehydration of the stream eliminates the need for repeated vaporization and liquefaction, leading to low separation energy consumption. The distillation process is conducted at atmospheric pressure and low temperature, resulting in fewer side reactions and a higher total yield of THF.

[0040] 4) For the scheme of removing residual water below 1% by BDO extractive distillation, the system's own raw material BDO is used as the extractant. While recovering BDO, a small amount of anhydrous BDO is added for extractive distillation to further remove the residual water below 1% in THF after liquid phase membrane dehydration, reducing the product water content to below 100 ppm. There is no need to add a new separation tower to separate the residual water below 1%, reducing equipment investment. Moreover, compared with the traditional extractive distillation process, no new extractant is added, avoiding the separation and recovery of the extractant.

[0041] 5) The invented fixed-bed reactor is specially designed so that the BDO feedstock uniformly passes radially (laterally) through the catalyst bed for reaction, then collects at the top of the reactor, and is discharged from the reactor as a liquid phase after being back-pressurized by a back-pressure valve. This reactor can greatly reduce the bed pressure drop, avoid bed blockage, and ensure the best reaction effect of BDO cyclization to THF. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the system and process for preparing tetrahydrofuran from 1,4-butanediol according to a preferred embodiment of the present invention.

[0043] Figure 2 This is a schematic cross-sectional view of the fixed-bed reactor in this invention.

[0044] Figure 3 This is a top view of the fixed-bed reactor in this invention.

[0045] Figure 4 This is a schematic diagram of the system and process for preparing tetrahydrofuran from 1,4-butanediol in another preferred embodiment of the present invention.

[0046] Figure 5 This is a schematic diagram of the system and process for preparing tetrahydrofuran from 1,4-butanediol in another preferred embodiment of the present invention.

[0047] Explanation of reference numerals in the attached figures: Device code: R1, fixed-bed reactor; PV1, liquid-phase membrane dehydration assembly; C1, BDO recovery tower; R2, hydrogenation reactor; C2, atmospheric dehydration tower; C3, heavy removal tower; R1-1, back pressure valve; R1-2, liquid distributor; R1-3, catalyst bed. Logistics code: 1. 1,4-Butanediol; 2. Liquid phase at the outlet of the fixed-bed reactor; 3. Discharge after liquid phase membrane dehydration; 4. Wastewater; 5. Circulating BDO; 6. Extractant BDO; 7. Top discharge from the BDO recovery tower; 8. Discharge from the hydrogenation reactor; 9. THF product; 10. Heavy oil; 11. Top discharge from the atmospheric dehydration tower; 12. Bottom discharge from the atmospheric dehydration tower. Detailed Implementation

[0048] 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.

[0049] like Figure 1 As shown, the system for preparing tetrahydrofuran from 1,4-butanediol provided by the present invention includes: a fixed-bed reactor R1, a liquid-phase membrane dehydration assembly PV1, a BDO recovery tower C1, a hydrogenation reactor R2, and a heavy removal tower C3 arranged in sequence.

[0050] Fixed-bed reactor R1: Its catalyst bed is filled with a solid acid catalyst (preferably a strongly acidic cation exchange resin catalyst). The bottom feed inlet is used to feed 1,4-butanediol 1 for cyclization and dehydration to produce tetrahydrofuran. A back pressure valve R1-1 (e.g., ...) is installed at the top discharge outlet. Figure 2 (As shown) to control the pressure inside the fixed-bed reactor so that all materials inside the reactor are in the liquid phase.

[0051] like Figure 2 and Figure 3 As shown, the fixed bed reactor R1 is preferably a radial fixed bed reactor, in which the catalyst bed R1-3 is packed in a circular manner coaxially with the reactor, and a liquid distributor R1-2 is provided at the middle position in the axial direction.

[0052] Traditional fixed-bed reactors are typically stacked-bed reactors, with reactants entering from the bottom and exiting from the top, or vice versa. The resin bed at the reactor inlet is subject to significant impact from the liquid phase and the reactants, leading to catalyst pulverization, high bed pressure drop, or blockage. This is especially true for the catalyst particles used in this invention, which have a diameter of less than 0.2-1 mm, making bed blockage even more likely. Therefore, the fixed-bed reactor of this invention is specially designed for more uniform material distribution. BDO feedstock enters the intermediate liquid distributor R1-2 from the bottom of the annularly packed reactor. Under the action of the distributor, the BDO feedstock uniformly passes radially (laterally) through the catalyst bed R1-3 for reaction, then collects at the top of the reactor and exits as a liquid phase after being pressurized by the back pressure valve. This reactor significantly reduces bed pressure drop, ensuring optimal reaction efficiency for the cyclization of BDO to THF.

[0053] Preferably, within the fixed-bed reactor R1, the reaction temperature is 80~140℃, more preferably 90~135℃, and even more preferably 100~125℃; the pressure is 0.2~1 MPaG, more preferably 0.2~0.7 MPaG, and even more preferably 0.4~0.6 MPaG; and the reaction space velocity is 0.5~4 h⁻¹. -1 More preferably 0.5~3 h -1Further preferably 0.5~2h -1 According to the system obtained by the present invention, preferably, the reaction temperature in the fixed-bed reactor is 100~120℃. The fixed-bed reactor R1 ensures that the cyclization products water and THF are both in the liquid phase through the dual conditions of back pressure valve R1-1 and reaction temperature.

[0054] Liquid phase membrane dehydration component PV1: Its inlet is connected to the top outlet of the fixed bed reactor R1, and the liquid phase 2 from the outlet of the fixed bed reactor directly enters the liquid phase membrane dehydration component PV1 for liquid phase membrane dehydration. Preferably, the temperature of the liquid phase membrane dehydration is 40~120℃, more preferably 50~110℃, and even more preferably 60~100℃; the pressure is 0~0.4 MPaG, more preferably 0.1~0.3 MPaG. The effluent 3 after liquid phase membrane dehydration is THF material with a water content of less than 1% (containing unreacted BDO raw material); wastewater 4 is discharged from the membrane permeation side.

[0055] Preferably, the feed water content of the liquid phase membrane dehydration component is 5%~30%, more preferably 10%~20%; the effluent water content on the osmotic side is 0.1%~1%, more preferably 0.2%~1%, and more preferably 0.2%~0.5%.

[0056] BDO Recovery Tower C1: The effluent outlet on the permeate side of the liquid membrane dehydration assembly PV1 is connected to the bottom inlet of the BDO recovery tower C1. After liquid membrane dehydration, the effluent 3 is sent to the BDO recovery tower C1 to complete BDO recovery. Extractant BDO 6 (fresh, anhydrous BDO) is injected from the top of the BDO recovery tower C1 for extractive distillation to remove residual water. The top effluent 7 of the BDO recovery tower is a THF stream with a water content of less than 100 ppm. The bottom material is recycled back to the fixed-bed reactor R1 as recycled BDO 5 for further reaction.

[0057] Preferably, the reflux ratio of the BDO recovery tower C1 is 0.2~4, more preferably 0.5~2; the operating pressure is 0~0.2 MPaG, and the tower bottom temperature is 67~160℃; the amount of extractant BDO 6 is 0.1~1 times the mass of the feed (output 3 after liquid phase membrane dehydration), more preferably 0.1~0.5 times; and the concentration of the 1,4-butanediol material (circulating BDO 5) obtained in the tower bottom is 70~99%, more preferably 90~99%.

[0058] Hydrogenation reactor R2: Its bottom inlet is connected to the top outlet of the BDO recovery tower. The top effluent 7 from the BDO recovery tower is sent to hydrogenation reactor R2 for hydrogenation of small amounts of unsaturated substances such as dihydrofuran. The dihydrofuran content in the effluent 8 from hydrogenation reactor R2 reaches below 2 ppm. Preferably, the catalyst for the hydrogenation reaction is a Cu-based or Ni-based catalyst. The preferred reaction temperature is 50~110℃, the preferred pressure is 0.5~1 MPaG, and the preferred reaction space velocity is 0.5~4 h⁻¹. -1 More preferably 0.5~2 h -1 .

[0059] Heavy oil removal tower C3: Its bottom inlet is connected to the top outlet of the hydrogenation reactor. The discharge from the hydrogenation reactor 8 then enters the heavy oil removal tower C3. At the top of the heavy oil removal tower C3, a polymer-grade THF product 9 with a purity greater than 99.9%, a water content less than 100 ppm, and a dihydrofuran content less than 2 ppm is obtained. A small amount of heavy oil 10 is discharged from the bottom of the heavy oil removal tower C3.

[0060] Preferably, the reflux ratio of the deweighting tower is 0.5~5, the operating pressure is 0~0.2 MPaG, and the tower bottom temperature is 67~100℃.

[0061] exist Figure 1 In the system and corresponding method, the BDO recovery tower C1 uses the system's own raw material BDO as the extractant. While recovering BDO, a small amount of anhydrous BDO is added for extractive distillation to further remove approximately 0.5% to 1% of water remaining in the THF after dehydration of the liquid phase membrane, reducing the product water content to below 100 ppm. This eliminates the need for an additional separation tower to separate the residual 0.5% to 1% water, reducing equipment investment. Furthermore, compared to traditional extractive distillation processes, no new extractant is added, avoiding the need for extractant separation and recovery.

[0062] like Figure 4 As shown, in another preferred embodiment of the present invention, the extractive distillation of BDO6 in the upper part of the BDO recovery tower C1 is replaced by an atmospheric dehydration tower C2. After BDO is recovered in the BDO recovery tower C1, the top effluent 7 of the BDO recovery tower enters the atmospheric dehydration tower C2 for atmospheric distillation to further remove residual water, which can also reduce the water content to below 100 ppm. The bottom effluent 12 of the atmospheric dehydration tower enters the hydrogenation reactor R2 for further processing, and the top effluent 11 of the atmospheric dehydration tower, which is THF with a water content of about 5%, is returned to the liquid phase membrane dehydration unit PV1.

[0063] Preferably, the temperature of the atmospheric dehydration tower C2 is 67~90℃. The bottom product 12 of the atmospheric dehydration tower enters the subsequent hydrogenation reactor R2 and the heavy oil removal tower C3 to further remove unsaturated substances and heavy oil, obtaining THF product 9.

[0064] In this scheme, the atmospheric dehydration tower C2 is combined with the liquid phase membrane separation component PV1. Membrane separation can easily reduce the water content from 20% to 0.5%~1%, requiring a small membrane area and low investment. By combining membrane separation with atmospheric separation, the water content can be reduced from 20% to 100 ppm while reducing the total equipment investment. At the same time, compared with ordinary high and low pressure distillation separation, atmospheric separation has a lower system pressure and lower operating temperature, which can reduce the loss of THF polymerization at high temperature and improve the overall product yield.

[0065] like Figure 5 As shown, in another preferred embodiment of the present invention, in Figure 4 Based on the previous scheme, the BDO recovery tower C1 is placed before the liquid-phase membrane dehydration component PV1. BDO is recovered first, followed by liquid-phase membrane dehydration, separating the cyclic reaction from THF separation, making the fixed-bed cyclization reaction operation more flexible. The main difference between placing the BDO recovery tower before and after the liquid-phase membrane dehydration component lies in the different performance requirements of the membrane. The latter requires the membrane to have higher acid resistance, while the former has slightly lower requirements.

[0066] Specifically, for the liquid phase membrane dehydration component PV1, since it uses a fully liquid phase feed, the liquid phase membrane used must have strong water resistance and a certain degree of acid resistance; a CHA separation membrane or a NaA type molecular sieve membrane can be selected. More specifically, for Figure 4 In this design, all reactants must enter the liquid-phase membrane dehydration module PV1. Since the materials contain a small amount of acidic impurities, the membrane needs high acid resistance; a CHA separation membrane is preferred. Figure 5 In terms of the solution, acidic impurities are separated by the BDO recovery tower C1, and the top discharge of the tower is almost free of acidic impurities. The requirements for the membrane are slightly lower, and the cheaper NaA molecular sieve membrane can be used.

[0067] The following are several application examples provided by the present invention for more specific illustration: Application Example 1 This application example provides Figure 1 A typical process of the solution: (1) 2 kg / h of BDO was introduced into the fixed-bed reactor R1 and subjected to a temperature of 0.5 MPaG, 110 °C, and a space velocity of 2 h⁻¹. -1 The reaction was carried out in a fully liquid phase, with a BDO conversion of 70%, a THF selectivity of greater than 99.5%, and the main impurity dihydrofuran less than 10 ppm.

[0068] (2) The feed composition of the fixed bed reactor R1 is about 30% BDO, 56% THF and 14% water. It enters the liquid phase membrane dehydration module PV1 directly at 110°C. The osmotic side obtains THF with a water content of less than 1%, and the permeate side discharges wastewater 4.

[0069] (3) The membrane outlet material enters the middle of BDO recovery tower C1. Fresh BDO extractant of about 1.4 kg / h is injected into the upper part of the tower. After separation in BDO recovery tower C1, the bottom of the tower yields BDO with a content of >99% which is recycled back to the fixed bed reactor R1 for further reaction. THF with dihydrofuran <20 ppm and water content of less than 0.01% is obtained at the top of the tower.

[0070] (4) The top material of the BDO recovery tower C1 enters the hydrogenation reactor R2 and is heated at 90°C, 0.8 MPaG, and space velocity 1 h⁻¹. -1 The reaction proceeded as follows, and no dihydrofuran was found in the THF outlet.

[0071] (5) The hydrogenation outlet material enters the de-heavy tower C3, and is separated at a reflux ratio of 0.5 and atmospheric pressure. THF with a water content of less than 0.01% and a purity of more than 99.9% is obtained at the top of the tower.

[0072] Application Example 2

[0073] This application example provides Figure 4 A typical process of the solution: (1) 2 kg / h of BDO was introduced into the fixed-bed reactor R1 and subjected to a temperature of 0.5 MPaG, 120 °C, and a space velocity of 2 h⁻¹. -1 The reaction was carried out in a completely liquid phase, with a BDO conversion rate of 80%, a THF selectivity of greater than 99.5%, and a major impurity, dihydrofuran, of less than 20 ppm.

[0074] (2) The feed composition of the fixed bed reactor R1 is about 20% BDO, 64% THF and 16% water. It enters the liquid phase membrane dehydration module PV1 directly at 120°C and the permeate side is THF with a water content of less than 0.5%.

[0075] (3) The membrane outlet material enters the middle of BDO recovery tower C1. After separation in tower C1, the bottom of the tower yields >99% BDO, which is recycled back to the fixed bed reactor R1 for further reaction. The top of the tower yields THF with dihydrofuran <20 ppm and water content less than 0.5%.

[0076] (4) The material at the top of the BDO recovery tower C1 enters the atmospheric dehydration tower C2 and is separated at a reflux ratio of 0.5. The bottom of the tower yields THF with a water content of less than 0.01%, and the top of the tower yields THF with a water content of 5% which is returned to the inlet of the liquid phase membrane dehydration component PV1.

[0077] (5) The bottom material of the atmospheric dehydration tower C2 enters the hydrogenation reactor R2 and is heated at 90°C, 0.8 MPaG, and space velocity 1 h⁻¹. -1 The reaction proceeded as follows, and no dihydrofuran was found in the THF outlet.

[0078] (6) The hydrogenation outlet material enters the de-heavy tower C3, and is separated at a reflux ratio of 0.5 and atmospheric pressure. THF with a water content of less than 0.01% and a purity of more than 99.9% is obtained at the top of the tower.

[0079] Application Example 3

[0080] This application example provides Figure 5 A typical process of the solution: (1) 2 kg / h of BDO was introduced into the fixed-bed reactor R1 and subjected to a temperature of 0.5 MPaG, 110 °C, and a space velocity of 2 h⁻¹. -1 The reaction was carried out in a liquid phase, with a BDO conversion rate of 70%, a THF selectivity of greater than 99.5%, and the main impurity dihydrofuran less than 10 ppm.

[0081] (2) The effluent composition of the fixed bed reactor R1 is approximately 30% BDO, 56% THF, and 14% water. It is directly fed into the BDO recovery tower C1 at 110°C. After separation in the BDO recovery tower C1, the effluent from the tower bottom is >99% BDO and recycled back to the fixed bed reactor R1 for further reaction.

[0082] (3) The top material of the BDO recovery tower includes about 20% water and 80% THF. After cooling, it is heated to 110°C in the liquid phase and enters the liquid phase membrane dehydration module PV1. The THF with a water content of less than 0.5% is obtained at the effluent outlet.

[0083] (4) The membrane outlet material directly enters the atmospheric pressure dehydration tower C2 and is separated at a reflux ratio of 0.5. The bottom of the tower obtains THF with a water content of less than 0.01%, and the top of the tower obtains THF with a water content of 5% and returns it to the inlet of the liquid phase membrane dehydration component PV1.

[0084] (5) The top material of the atmospheric dehydration tower C2 enters the hydrogenation reactor R2 and is heated at 90℃, 0.8MPaG, and space velocity 1 h⁻¹. -1 The reaction proceeded as follows, and no dihydrofuran was found in the THF outlet.

[0085] (6) The hydrogenation outlet material enters the de-heavy tower C3, and is separated at a reflux ratio of 0.5 and atmospheric pressure. THF with a water content of less than 0.01% and a purity of more than 99.9% is obtained at the top of the tower.

[0086] A THF production capacity of 1000 kg / h BDO is completely converted to generate 800 kg / h THF. The energy consumption data for the three application examples are calculated as shown in Table 1 below: Table 1

[0087] The energy-saving effect is better when one atmospheric pressure dehydration tower C2 is omitted in Application Example 1.

[0088] Comparative Example 1

[0089] This comparative example uses high- and low-pressure azeotropic distillation for tetrahydrofuran separation. The difference from Application Example 3 is that the top stream of the BDO recovery tower enters the azeotropic tower for water removal, the wastewater is discharged from the bottom of the azeotropic tower, and the top stream of the azeotropic tower enters the 0.8 MPaG pressurized tower. The top stream of the pressurized tower is returned to the azeotropic tower, and the bottom stream of the pressurized tower is then processed in the same way as in Application Example 3, entering the hydrogenation reactor R2 and the deweighting tower C3.

[0090] Comparative Example 2

[0091] In this comparative example, a pervaporation membrane dehydration is used instead of the liquid phase membrane dehydration component PV1 in Application Example 3. After the BDO is recovered from the reaction, the material needs to be cooled and then revaporated before entering the gas phase membrane separation component for separation.

[0092] Comparative Examples 1 and 2, as well as Application Example 3, all used different processes with a THF treatment load of 800 kg / h. The energy consumption of the different processes is compared in Table 2. As can be seen from the comparison in Table 2, the liquid phase membrane dehydration process of the present invention is more energy-efficient than the gas phase membrane dehydration process.

[0093] Table 2

[0094] 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 system for preparing tetrahydrofuran from 1,4-butanediol, wherein, The system includes the following components set in sequence: Fixed-bed reactor: Its catalyst bed is filled with solid acid catalyst, and the bottom feed port is used to feed 1,4-butanediol for cyclization and dehydration reaction to produce tetrahydrofuran. The discharge port is equipped with a back pressure valve to control the pressure inside the fixed-bed reactor so that all materials in the reactor are in the liquid phase. Liquid phase membrane dehydration assembly: its inlet is connected to the top outlet of the fixed bed reactor; BDO Recovery Tower: The osmotic side outlet of the liquid phase membrane dehydration component is connected to the bottom inlet of the BDO recovery tower; the BDO recovery tower uses 1,4-butanediol to enter from the top of the tower for extractive distillation to remove residual water from the material, and the top outlet of the tower yields a THF stream with a water content of less than 100 ppm, and the bottom material is recycled back to the fixed bed reactor for further reaction; Hydrogenation reactor: Its bottom inlet is connected to the top outlet of the BDO recovery tower; Heavy removal tower: Its bottom inlet is connected to the top outlet of the hydrogenation reactor, and the top outlet of the tower yields polymer-grade THF product.

2. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 1, wherein, The fixed-bed reactor is a radial fixed-bed reactor, in which the catalyst bed is packed in a circular manner coaxially with the reactor, and a liquid distributor is set at the middle position of the axial direction.

3. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 2, wherein, The temperature inside the fixed-bed reactor is set at 80~140℃.

4. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 1, wherein, The solid acid catalyst is a strong acid cation exchange resin catalyst.

5. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 1, wherein, The membrane in the liquid phase membrane dehydration assembly is a CHA separation membrane or a NaA type molecular sieve membrane.

6. The system for preparing tetrahydrofuran from 1,4-butanediol according to any one of claims 1-5, wherein, The BDO recovery tower eliminates the 1,4-butanediol feed at the top of the tower, and the system is equipped with an atmospheric dehydration tower after the BDO recovery tower and before the hydrogenation reactor; The top outlet of the BDO recovery tower is connected to the bottom inlet of the atmospheric dehydration tower, the bottom outlet of the atmospheric dehydration tower is connected to the bottom inlet of the hydrogenation reactor, and the top outlet is connected to the inlet of the liquid membrane dehydration assembly.

7. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 6, wherein, The set temperature of the atmospheric pressure dehydration tower is 67~90℃.

8. The system for preparing tetrahydrofuran from 1,4-butanediol according to claim 6, wherein, The BDO recovery tower is located before the liquid phase membrane dehydration assembly; The top outlet of the fixed-bed reactor is connected to the bottom inlet of the BDO recovery tower, the top outlet of the BDO recovery tower is connected to the inlet of the liquid membrane dehydration assembly, and the osmosis side outlet of the liquid membrane dehydration assembly is connected to the bottom inlet of the atmospheric pressure dehydration tower.

9. A method for preparing tetrahydrofuran from 1,4-butanediol, wherein, This method is accomplished using the system described in any one of claims 1-8. Includes the following processes: 1,4-Butanediol enters a fixed-bed reactor for cyclization and dehydration to produce tetrahydrofuran. The top discharge from the fixed-bed reactor enters the liquid phase membrane dehydration unit in liquid phase form for liquid phase membrane dehydration. THF material with a water content of 0.5%~1% is obtained on the permeate side, and wastewater is discharged from the permeate side. The effluent from the permeate side of the liquid membrane dehydration unit is sent to the BDO recovery tower, and 1,4-butanediol is fed from the top of the tower for extractive distillation to recover 1,4-butanediol and remove residual water. The 1,4-butanediol material obtained in the bottom of the tower is recycled back to the fixed bed reactor for further reaction, and qualified dehydrated THF is obtained from the top outlet of the tower. The dehydrated THF stream is sent to the hydrogenation reactor to hydrogenate the small amount of unsaturated matter in the THF. The top outlet yields THF material with an unsaturated matter content of less than 2 ppm. It then enters the de-heavy tower, where polymer-grade THF product is obtained at the top outlet, and a small amount of waste oil is discharged from the tower bottom.

10. The method according to claim 9, wherein, The reaction temperature in the fixed-bed reactor is 80~140℃, and the pressure is 0.2~1 MPaG.

11. The method according to claim 9, wherein, The reaction space velocity of the fixed-bed reactor is 0.5~4 h. -1 .

12. The method according to claim 9, wherein, The liquid phase membrane dehydration temperature is 40~120℃, and the pressure is 0~0.4MPaG.

13. The method according to claim 9, wherein, The liquid phase membrane dehydration unit has a feed water content of 5% to 30% and an output water content of 0.1% to 1%. The BDO recovery tower has a reflux ratio of 0.2 to 4; an operating pressure of 0 to 0.2 MPaG; and a reboiler temperature of 67 to 160°C. The amount of 1,4-butanediol entering from the top of the column is 0.1 to 1 times the feed mass, and the concentration of 1,4-butanediol obtained from the bottom of the column is 70 to 99%.

14. The method according to claim 9, wherein, The hydrogenation reaction is carried out using a Cu-based or Ni-based catalyst, at a reaction temperature of 50–110 °C, a pressure of 0.5–1 MPaG, and a space velocity of 0.5–4 h⁻¹. -1 .

15. The method according to claim 9, wherein, The reflux ratio of the deweight removal tower is 0.5~5, the operating pressure is 0~0.2MPaG, and the tower bottom temperature is 67~100℃.

16. The method according to any one of claims 9-15, wherein, In the method described, the feeding of 1,4-butanediol from the top of the BDO recovery tower is eliminated, and after BDO recovery, the material obtained from the top outlet of the BDO recovery tower is sent to an atmospheric dehydration tower for atmospheric dehydration to remove residual water; then it enters the subsequent hydrogenation reactor and deweighting tower.

17. The method according to claim 16, wherein, The temperature for atmospheric pressure dehydration is 67~90℃.

18. The method according to claim 16, wherein, In the method described above, BDO is first recovered, followed by liquid membrane dehydration.

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