阅读说明：本技术 一种高生产效率的聚四亚甲基醚二醇制备方法 (High-production-efficiency preparation method of polytetramethylene ether glycol ) 是由 施可彬 易杰 于 2020-04-21 设计创作，主要内容包括：本发明涉及化工领域,公开了一种高生产效率的聚四亚甲基醚二醇制备方法,包括：1)将添加有乙醚的四氢呋喃和催化剂经强化分散器混合,并在50~52℃下进行聚合反应；2)反应液通过离心将催化剂分离；3)剩余反应液经蒸馏将大部分四氢呋喃及全部乙醚去除；浓缩液与萃取剂混合后离心；4)剩余混合液经吸附柱吸附后,催化剂被彻底去除,再通过蒸馏将四氢呋喃去除；5)剩余混合液在38℃进行沉降分离,经过精制器处理后得到聚四亚甲基醚二醇。本发明一方面通过在四氢呋喃中加入适量乙醚,另一方面通过强化分散器,提高催化剂分散度以提升反应速度,通过循环换热适当降低反应温度提高平衡转化率从而提升聚四亚甲基醚二醇产量上限。(The invention relates to the field of chemical industry, and discloses a preparation method of polytetramethylene ether glycol with high production efficiency, which comprises the following steps: 1) mixing tetrahydrofuran added with diethyl ether and a catalyst by a reinforced disperser, and carrying out polymerization reaction at 50-52 ℃; 2) separating the catalyst from the reaction solution by centrifugation; 3) distilling the residual reaction liquid to remove most tetrahydrofuran and all diethyl ether; mixing the concentrated solution with an extracting agent and then centrifuging; 4) adsorbing the residual mixed solution by an adsorption column, completely removing the catalyst, and removing tetrahydrofuran by distillation; 5) and settling and separating the residual mixed solution at 38 ℃, and treating by a refiner to obtain the polytetramethylene ether glycol. According to the invention, on one hand, a proper amount of diethyl ether is added into tetrahydrofuran, on the other hand, the dispersion degree of the catalyst is improved by strengthening the disperser so as to improve the reaction speed, and the reaction temperature is properly reduced by circulating heat exchange so as to improve the equilibrium conversion rate, so that the upper limit of the yield of the polytetramethylene ether glycol is improved.)

1. A preparation method of polytetramethylene ether glycol with high production efficiency is characterized by comprising the following steps:

1) fully mixing tetrahydrofuran added with diethyl ether and a catalyst through an enhanced disperser, keeping the temperature at 50-52 ℃, and then feeding into a main reaction kettle for polymerization reaction; the reinforced disperser consists of a static mixing section, a distribution plate and a circulating heat exchange section from bottom to top in sequence;

2) the catalyst settled in the main reaction kettle is sent out from the bottom of the kettle for recycling, the obtained reaction liquid is discharged from the top of the kettle and then enters a primary centrifuge, and most of the catalyst is separated and recycled through the centrifugal action;

3) the residual reaction solution enters a first distillation tower to remove most tetrahydrofuran and all diethyl ether, and the tetrahydrofuran content in the obtained concentrated solution is kept at 25-35 wt%; discharging the concentrated solution from the bottom of the first distillation tower, mixing the concentrated solution with an extractant, feeding the mixture into a secondary centrifuge, wherein the concentration of the extractant in the mixed solution is 55-65 wt%, and separating and recycling the catalyst separated out under the action of the extractant by the secondary centrifuge;

4) the catalyst is thoroughly removed after the residual mixed solution containing a small amount of catalyst is adsorbed by the adsorbent in the adsorption column; removing tetrahydrofuran from the mixed solution by a second distillation tower, wherein the mixed solution after the catalyst is removed mainly contains tetrahydrofuran, an extracting agent and polytetramethylene ether glycol;

5) the mixed solution containing the extractant and the polytetramethylene ether glycol enters a settling separator to be layered at the temperature of 35-40 ℃, the extractant on the upper layer is collected and recycled, and the material on the lower layer is conveyed to a refiner to remove residual solvent to obtain pure polytetramethylene ether glycol.

2. The method of claim 1, wherein in step 1):

the heteropoly acid catalyst is phosphotungstic heteropoly acid, and the volume content of the catalyst in the reaction liquid is 35-40%; and/or

The content of diethyl ether in the tetrahydrofuran is 1-1.5 wt%; and/or

The charging coefficient of the main reaction kettle is 100 percent.

3. The production method according to claim 1 or 2, wherein in the step 1), in the polymerization reaction in the main reaction vessel, an alternating pulsed magnetic field is applied to the reaction system in the main reaction vessel; the catalyst is phosphotungstic heteropoly acid compounded with ferroferric oxide magnetic powder; and the particle size of the catalyst comprises a plurality of micron-sized segments.

4. The preparation method according to claim 3, wherein in the step 1), the phosphotungstic heteropoly acid compounded with the ferroferric oxide magnetic powder is prepared by the following steps:

(a) weighing sodium pyrophosphate, methyl hydroxyethyl cellulose and a silane coupling agent KH550 according to the weight ratio of 2-3:2-3:1, adding into 10-15 times of deionized water, heating in water bath to 50-55 ℃, and ultrasonically dispersing for 30-40min to obtain viscous liquid;

(b) adding 1-3wt% of attapulgite into the prepared viscous liquid, and shearing and dispersing at the high speed of 2500rpm of 2000-20 min to obtain attapulgite modified viscous liquid;

(c) uniformly spraying 55-65 parts by weight of the modified viscous liquid prepared in the step (c) onto 100-130 parts by weight of ferroferric oxide powder;

(d) drying the product obtained in the step (c) at the temperature of 80-90 ℃, then heating to 110-;

(e) according to the weight ratio of 5-8:4-5:3-4, stirring and mixing tetrahydrofuran, ferroferric oxide and phosphotungstic heteropoly acid at a low speed at 40-50 ℃, standing until a system is layered after mixing is finished, and taking a lower fluidized part to obtain the phosphotungstic heteropoly acid compounded with ferroferric oxide magnetic powder.

5. The method according to claim 3, wherein in the step 2) and the step 3), a constant magnetic field is applied to promote separation of the catalyst during centrifugal separation of the catalyst.

6. The preparation method according to claim 1, wherein in the step 3), the extracting agent is n-octane, and the extraction temperature is 68-73 ℃.

7. The method of claim 1, wherein in step 4), the adsorbent is 20-40 mesh silica gel or coconut shell activated carbon.

8. The method according to claim 1, wherein in the step 4), the refining temperature of the refiner is 155 to 165 ℃.

9. The production method according to claim 1, wherein the polytetramethylene ether glycol is produced by a polytetramethylene ether glycol production line comprising an intensive disperser, a main reaction vessel, a primary centrifuge, a first distillation column, a secondary centrifuge, an adsorption column, a second distillation column, a settling separator and a refiner, which are connected in this order; the reinforced disperser is composed of a static mixing section, a distribution plate and a circulating heat exchange section from bottom to top in sequence.

10. The preparation method of claim 9, wherein a catalyst return line for returning to the static mixing section is arranged on the bottom of the main reaction kettle, the primary centrifuge and the secondary centrifuge; tetrahydrofuran reflux pipelines which reflux to the static mixing section are arranged at the tops of the first distillation tower and the second distillation tower; and/or

Through holes with the diameter of 0.5-1 mm are formed in the distribution plate; and/or

The static mixing section consists of horizontal SV type mixing units and vertical SV type mixing units which are arranged at intervals; the distribution plate is arranged at the top of the static mixing section.

Technical Field

The invention relates to the field of chemical industry, in particular to a preparation method of polytetramethylene ether glycol with high production efficiency.

Background

Polytetramethylene ether glycol, prepared by cationic ring-opening polymerization of Tetrahydrofuran (THF) in the earliest 30s of the 20 th century. The synthesis reaction formula is as follows:

nC₄H₈O+H₂o ═ HO ═ C (initiator) ═ HO ═ C₄H₈O-]_n-H

The polytetramethylene ether glycol is usually synthesized by an acetic anhydride-perchloric acid method, a concentrated sulfuric acid method, a fluorosulfonic acid method, a clay method, a heteropoly acid method, or the like. With the increasing awareness of environmental protection and the consideration of process and product quality, the heteropolyacid method is receiving more attention and application.

The Chinese invention with the patent number of CN00811571.0 discloses a method for producing polytetramethylene ether glycol, which mainly discloses a method for producing the polytetramethylene ether glycol with high temperature resistance and low viscosity. The method focuses on improving the technical process from the aspect of product performance, and effectively improves the high temperature resistance and low viscosity performance of the polytetramethylene ether glycol.

The applicant's prior application CN201811562612.4 discloses a method for simultaneously preparing polytetramethylene ether glycol with various specifications, comprising: 1) adding tetrahydrofuran, then adding a heteropoly acid catalyst, stirring, mixing and reacting for 3-5 hours; 2) stopping stirring, standing to form a lower catalyst phase and an upper organic phase, and replacing the upper organic phase with tetrahydrofuran with the moisture of less than 0.1% to adjust the specific gravity of the heteropoly acid catalyst in the organic phase to 1.8-2.0 g/cm³(ii) a 3) Continuously introducing tetrahydrofuran; after the reaction kettle is filled with the polymerization solution, the polymerization solution enters a settling separation tank; 4) settling for 1-3 hours in a settling separation tank, and inputting the reaction liquid subjected to settling separation into a tetrahydrofuran distillation tower; 5) adding an extracting agent into a tetrahydrofuran distillation tower, and mixing and extracting the extracting agent and the reaction liquid subjected to settling separation; 6) and conveying the extracted mixed liquid to a polymer separator for separation. The method realizes the simultaneous preparation of polytetramethylene ether glycol with different specifications.

Although the prior art including the above patent applications have disclosed various processes for producing polytetramethylene ether glycol, no intensive research and improvement has been made on how to improve the polymerization efficiency of polytetramethylene ether glycol, and thus there is a need for a process for producing polytetramethylene ether glycol with high production efficiency.

Disclosure of Invention

In order to solve the technical problems, the invention provides a preparation method of polytetramethylene ether glycol with high production efficiency, and the invention mainly optimizes the aspects of catalyst dispersion effect, reaction conversion rate, catalyst separation effect and the like so as to improve the production efficiency of polytetramethylene ether glycol. Specifically, on one hand, a proper amount of diethyl ether is added into tetrahydrofuran as a raw material, on the other hand, a traditional stirring mode is replaced by an enhanced disperser, the catalyst dispersion degree is improved so as to improve the reaction speed, and the reaction temperature is properly reduced through circulating heat exchange so as to improve the equilibrium conversion rate, so that the upper limit of the yield of the polytetramethylene ether glycol is improved. The application of the centrifuge greatly improves the catalyst separation efficiency, thereby increasing the system processing capacity and having better economy.

The specific technical scheme of the invention is as follows: a preparation method of polytetramethylene ether glycol with high production efficiency comprises the following steps:

1) fully mixing tetrahydrofuran added with diethyl ether and a heteropoly acid catalyst through a strengthening disperser, keeping the temperature at 50-52 ℃, and then entering a main reaction kettle for polymerization reaction; the reinforced disperser is composed of a static mixing section, a distribution plate and a circulating heat exchange section from bottom to top in sequence.

2) And (3) sending the catalyst settled in the main reaction kettle out from the bottom of the kettle for recycling, discharging the obtained reaction liquid from the top of the kettle, and then sending the reaction liquid into a primary centrifuge, and separating and recycling most of the catalyst through the centrifugal action.

3) The residual reaction solution enters a first distillation tower to remove most tetrahydrofuran and all diethyl ether, and the tetrahydrofuran content in the obtained concentrated solution is kept at 25-35 wt%; and discharging the concentrated solution from the bottom of the first distillation tower, mixing the concentrated solution with an extractant, feeding the mixture into a secondary centrifuge, wherein the concentration of the extractant in the mixed solution is 55-65 wt%, and separating and recycling the catalyst separated out under the action of the extractant by the secondary centrifuge.

4) The catalyst is thoroughly removed after the residual mixed solution containing a small amount of catalyst is adsorbed by the adsorbent in the adsorption column; the mixed liquid from which the catalyst was removed mainly contains tetrahydrofuran, an extractant, and polytetramethylene ether glycol, and the tetrahydrofuran was removed by passing through a second distillation column.

5) The mixed solution containing the extractant and the polytetramethylene ether glycol enters a settling separator to be layered at the temperature of 35-40 ℃, the extractant on the upper layer is collected and recycled, and the material on the lower layer is conveyed to a refiner to remove residual solvent to obtain pure polytetramethylene ether glycol.

Tetrahydrofuran (THF) cationic ring-opening polymerization to polytetramethylene ether glycol, THF polymerization is an equilibrium polymerization process. The invention has found through previous studies that each temperature corresponds to a monomer concentration Mc, which is determined by the thermodynamics of polymerization. When the limiting temperature Te is reached, the monomeric THF is no longer polymerized. The Te for the bulk polymerization of THF was 85 ℃. + -. 2 ℃. The relationship between the THF concentration [ M ] c and the thermodynamic temperature T at equilibrium for the polymerization is:

ln[M]c＝ΔHp/RT-ΔSp/R＝ΔGp/RT

wherein R is a gas constant; Δ Hp is the enthalpy of polymerization; Δ Sp is the entropy change of [ M ] ═ 1 mol/L; Δ Gp is the free energy of polymerization at temperature T and atmospheric pressure. In order to obtain a higher polymerization conversion, it is important to select a suitable polymerization temperature and to limit the amount of solvent. The effect of temperature on the maximum conversion of tetrahydrofuran at equilibrium during bulk polymerization of tetrahydrofuran is shown in FIG. 4.

At temperatures below Te there is an equilibrium monomer concentration below which polymerization cannot proceed. The relationship between the THF equilibrium concentration and the temperature is shown in FIG. 5.

As shown in FIG. 5, for the polymerization of THF, the conversion of polytetramethylene ether glycol at a given polymerization temperature is thermodynamically controlled, depending on the concentration of monomer, independent of the concentration of polymer.

In view of the above, in order to increase the conversion per pass, it is necessary to appropriately lower the reaction temperature. Meanwhile, the activity of the catalyst is ensured, so that the catalyst is as close to a reaction equilibrium point as possible in a short reaction time.

Analyzing influence factors: factors affecting the activity of the catalyst are mainly reaction temperature, catalyst concentration, catalyst surface area, reaction time and the like.

a reaction temperature: the higher the reaction temperature, the faster the reaction rate. However, from the above analysis, the higher the temperature, the lower the equilibrium conversion. To obtain higher conversion, the temperature needs to be lowered appropriately, and the reaction rate is also slowed.

b catalyst concentration: within a certain range, the higher the catalyst concentration, the more active centers and the faster the reaction rate.

c catalyst surface area: the polymerization reaction takes place between the monomeric THF and the catalyst. Therefore, the larger the surface area of the catalyst, the more favorable the activity of the catalyst, and the faster the reaction speed. In the prior heteropoly acid process, a stirrer is used for mixing the catalyst, so that the dispersity is low and the surface area of the catalyst is small.

d, reaction time: after the reaction temperature was fixed, the maximum equilibrium conversion was also determined. But whether the equilibrium conversion is reached as far as possible within a particular reaction time (depending on the reactor size) is still dependent on the reaction rate.

Therefore, the invention improves the production efficiency from the following aspects:

in step 1): compared with the prior art which adopts a traditional mechanical stirring mode, the invention adopts the reinforced disperser with a three-section structure, can effectively improve the dispersion degree of the catalyst to improve the reaction speed, and simultaneously properly reduces the reaction temperature through circulating heat exchange to improve the equilibrium conversion rate so as to improve the upper limit of the yield of the polytetramethylene ether glycol.

The reinforced disperser is integrated with a static mixing section, a distribution plate and a circulating heat exchange section, and materials in the structure are regulated to a proper reaction temperature immediately after being reinforced and dispersed by the static mixer so as to achieve an optimal reaction state. The circulating heat exchange section is a tube-plate type heat exchange section, and the external circulating water and hot water pipeline can be cooled or heated according to the temperature requirement of the reaction liquid.

In addition, the invention adds a proper amount of ether in the system, in the reaction system of heteropoly acid and THF, the content of heteropoly acid which can be really dissolved in THF is less than 2%, and the fluidized catalyst can be separated from THF immediately when in rest due to the difference of specific gravity (the specific gravity of the catalyst is 1.8-2.2g/ml, and the THF is 0.89 g/ml). The solubility of the heteropoly acid in the ether is more than 50 percent, and the ether and the THF are miscible, so that a certain amount of ether is added, the solubility of the heteropoly acid in the mixed solution is greatly improved, the contact probability of the THF and the heteropoly acid catalyst is improved, and the reaction efficiency is improved.

On the other hand, the normal use range of the number average molecular weight of the PTMEG product is 1000-2000, and the catalyst activity is reduced and the molecular weight is out of control due to the excessively low temperature, so that the polymerization temperature is strictly controlled within 50-52 ℃, the reaction efficiency can be greatly improved, and the number average molecular weight is ensured to be within a reasonable range.

Step 2) and step 3): the application of the centrifuge greatly improves the catalyst separation efficiency, thereby increasing the system processing capacity and having better economy.

Preferably, in step 1): the heteropoly acid catalyst is phosphotungstic heteropoly acid, and the volume content of the catalyst in the reaction liquid is 35-40%.

Preferably, in step 1): the content of diethyl ether in the tetrahydrofuran is 1-1.5 wt%.

Preferably, in step 1): the charging coefficient of the main reaction kettle is 100 percent.

The filling factor of the main reaction kettle in the work is 100 percent, so that the reaction time is prolonged under the same volume condition to improve the conversion rate. And is beneficial to the sedimentation and recovery of the catalyst. The bottom of the kettle is connected with a catalyst recycling pipeline, and reaction liquid is discharged from the top of the kettle.

Preferably, in the step 1), during the polymerization reaction in the main reaction kettle, an alternating pulse magnetic field is applied to the reaction system in the main reaction kettle; the catalyst is phosphotungstic heteropoly acid compounded with micron-sized ferroferric oxide magnetic powder. And the particle size of the catalyst comprises a plurality of micron-sized segments.

Although the raw material and the catalyst are subjected to mixing and dispersing treatment by the enhanced disperser before entering the main reaction kettle, the catalyst is still gradually settled during the polymerization reaction in the main reaction kettle, so that the contact time and the contact area of the catalyst and the raw material are gradually reduced. In order to delay the phenomenon as much as possible, the invention firstly carries out composite 'binding' on the catalyst and the magnetic powder, then a magnetic field generating device is arranged on the main reaction kettle, an alternating and pulse magnetic field is applied during the polymerization reaction, and the invention has the following functions: firstly, the magnetic powder can be controlled to move back and forth in the kettle, the contact time with the raw material is prolonged, the sedimentation effect is delayed, and the catalysis time is prolonged; the collision probability among the catalysts is increased, and because the particle size of the catalyst is divided into a plurality of sections, the resistance received during movement is different, and speed difference is generated, so that the surface energy of the catalyst can be increased after high-speed collision, and the catalytic activity is enhanced.

Preferably, the particle size distribution of the catalyst is: 10-50 microns in the weight ratio of 40-60%, 80-120 microns in the weight ratio of 25-45%, 100-200 microns in the weight ratio of 10-20%,

preferably, the magnetic field strength is 0.1-2T, the alternation interval is 1-10 s, and the pulse interval is 20-60 s.

Under the magnetic field setting, the dispersity and the catalytic efficiency of the catalyst can be effectively improved.

Preferably, the preparation method of the phosphotungstic heteropoly acid compounded with the ferroferric oxide magnetic powder comprises the following steps:

(a) weighing sodium pyrophosphate, methyl hydroxyethyl cellulose and a silane coupling agent KH550 according to the weight ratio of 2-3:1, adding into 10-15 times of deionized water, heating in water bath to 50-55 ℃, and ultrasonically dispersing for 30-40min to obtain viscous liquid;

(b) adding 1-3wt% of attapulgite into the prepared viscous liquid, and shearing and dispersing at the high speed of 2500rpm of 2000-20 min to obtain attapulgite modified viscous liquid;

(c) uniformly spraying 55-65 parts by weight of the modified viscous liquid prepared in the step (c) onto 100-130 parts by weight of ferroferric oxide powder;

(d) drying the product obtained in the step (c) at the temperature of 80-90 ℃, then heating to 110-;

(e) according to the weight ratio of 5-8:4-5:3-4, stirring and mixing tetrahydrofuran, ferroferric oxide and phosphotungstic heteropoly acid at a low speed at 40-50 ℃, standing until the system is layered after mixing is finished, and taking the lower fluidized part to obtain the phosphotungstic heteropoly acid compounded with the ferroferric oxide magnetic powder.

Preferably, in step 2) and step 3), a constant magnetic field is applied to facilitate the separation of the catalyst when the catalyst is centrifugally separated.

The invention makes full use of the characteristics of magnetic powder, and when the catalyst is recovered, the catalyst can be quickly and efficiently recovered by applying a constant magnetic field.

Preferably, in the step 3), the extracting agent is n-octane, and the extraction temperature is 58-63 ℃.

Preferably, in the step 4), the adsorbent is 20-40 mesh silica gel or coconut shell activated carbon.

Preferably, in the step 4), the refining temperature of the refiner is 155-165 ℃. The temperature is more favorable for removing impurities with low boiling points.

Preferably, the polytetramethylene ether glycol is prepared by a polytetramethylene ether glycol production line, and the polytetramethylene ether glycol production line comprises an enhanced disperser, a main reaction kettle, a primary centrifuge, a first distillation tower, a secondary centrifuge, an adsorption column, a second distillation tower, a settling separator and a static device which are connected in sequence. The reinforced disperser is composed of a static mixing section, a distribution plate and a circulating heat exchange section from bottom to top in sequence.

The separator is provided with a clapboard inside, the mixed materials are layered at a certain temperature, and the extractant with low specific gravity overflows from the upper part of the clapboard and is recovered. PTMEG of high specific gravity is carried to the refiner with the extractant. And completely removing lower boiling point impurities such as an extractant and the like in a refining device at high temperature to obtain pure PTMEG.

Preferably, catalyst return pipelines which return to the static mixing section are arranged at the bottom of the main reaction kettle, the primary centrifugal machine and the secondary centrifugal machine.

Preferably, tetrahydrofuran reflux pipelines which reflux to the static mixing section are arranged at the tops of the first distillation tower and the second distillation tower.

Preferably, the distribution plate is provided with through holes with the diameter of 0.5-1 mm.

Preferably, the static mixing section is composed of horizontal SV type mixing units and vertical SV type mixing units which are arranged at intervals.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention improves the conversion efficiency by strictly controlling the reaction temperature.

(2) The invention improves the dispersibility of the catalyst by adding a proper amount of diethyl ether into tetrahydrofuran as a raw material.

(3) The invention improves the catalyst dispersion degree to improve the reaction speed by replacing the traditional stirring mode with the reinforced disperser, and properly reduces the reaction temperature by circulating heat exchange to improve the equilibrium conversion rate so as to improve the upper limit of the yield of the polytetramethylene ether glycol. The application of the centrifuge greatly improves the catalyst separation efficiency, thereby increasing the system processing capacity and having better economy.

(4) The invention improves the dispersibility and catalytic activity of the catalyst by modifying the catalyst and applying a magnetic field in a matching way.

Drawings

FIG. 1 is a schematic view showing the connection of polytetramethylene ether glycol of the present invention through a polytetramethylene ether glycol production line;

FIG. 2 is a schematic structural diagram of a static mixing section according to the present invention;

FIG. 3 is a distribution diagram of a via structure of a distribution plate according to the present invention;

FIG. 4 is a graph of the effect of temperature on the maximum conversion of tetrahydrofuran at equilibrium during bulk polymerization of tetrahydrofuran;

FIG. 5 is a graph showing the relationship between the equilibrium concentration of THF and temperature.

The reference signs are: the system comprises an intensified disperser 1, a main reaction kettle 2, a primary centrifuge 3, a first distillation tower 4, a secondary centrifuge 5, an adsorption column 6, a second distillation tower 7, a settling separator 8, a static device 9, a catalyst return pipeline 10, a tetrahydrofuran return pipeline 11, a through hole 12, a horizontal SV type mixing unit 13, a vertical SV type mixing unit 14, a static mixing section 15, a distribution plate 16 and a circulating heat exchange section 17.

Detailed Description

The present invention will be further described with reference to the following examples.

General examples

A preparation method of polytetramethylene ether glycol with high production efficiency comprises the following steps:

1) fully mixing tetrahydrofuran added with diethyl ether and a heteropoly acid catalyst through a strengthening disperser, keeping the temperature at 50-52 ℃, and then entering a main reaction kettle for polymerization reaction; the reinforced disperser is composed of a static mixing section, a distribution plate and a circulating heat exchange section from bottom to top in sequence.

2) And (3) sending the catalyst settled in the main reaction kettle out from the bottom of the kettle for recycling, discharging the obtained reaction liquid from the top of the kettle, and then sending the reaction liquid into a primary centrifuge, and separating and recycling most of the catalyst through the centrifugal action.

3) The residual reaction solution enters a first distillation tower to remove most tetrahydrofuran and all diethyl ether, and the tetrahydrofuran content in the obtained concentrated solution is kept at 25-35 wt%; and discharging the concentrated solution from the bottom of the first distillation tower, mixing the concentrated solution with an extractant, feeding the mixture into a secondary centrifuge, wherein the concentration of the extractant in the mixed solution is 55-65 wt%, and separating and recycling the catalyst separated out under the action of the extractant by the secondary centrifuge.

4) The catalyst is thoroughly removed after the residual mixed solution containing a small amount of catalyst is adsorbed by the adsorbent in the adsorption column; the mixed liquid from which the catalyst was removed mainly contains tetrahydrofuran, an extractant, and polytetramethylene ether glycol, and the tetrahydrofuran was removed by passing through a second distillation column.

5) The mixed solution containing the extractant and the polytetramethylene ether glycol enters a settling separator to be layered at the temperature of 35-40 ℃, the extractant on the upper layer is collected and recycled, and the material on the lower layer is conveyed to a refiner to remove residual solvent to obtain pure polytetramethylene ether glycol.

Preferably, in step 1): the heteropoly acid catalyst is phosphotungstic heteropoly acid, and the volume content of the catalyst in the reaction liquid is 35-40%. The content of diethyl ether in the tetrahydrofuran is 1-1.5 wt%. The charging coefficient of the main reaction kettle is 100 percent.

Preferably, in the step 1), during the polymerization reaction in the main reaction kettle, an alternating pulse magnetic field is applied to the reaction system in the main reaction kettle; the catalyst is phosphotungstic heteropoly acid compounded with ferroferric oxide magnetic powder. Preferably, the particle size distribution of the catalyst is: 10-50 microns in the range of 40-60 wt%, 80-120 microns in the range of 25-45 wt%, and 100-200 microns in the range of 10-20 wt%, preferably, the magnetic field strength is 0.1-2T, the alternation interval is 1-10 s, and the pulse interval is 20-60 s.

Preferably, the preparation method of the phosphotungstic heteropoly acid compounded with the ferroferric oxide magnetic powder comprises the following steps:

(a) weighing sodium pyrophosphate, methyl hydroxyethyl cellulose and a silane coupling agent KH550 according to the weight ratio of 2-3:1, adding into 10-15 times of deionized water, heating in water bath to 50-55 ℃, and ultrasonically dispersing for 30-40min to obtain viscous liquid;

(b) adding 1-3wt% of attapulgite into the prepared viscous liquid, and shearing and dispersing at the high speed of 2500rpm of 2000-20 min to obtain attapulgite modified viscous liquid;

(c) uniformly spraying 55-65 parts by weight of the modified viscous liquid prepared in the step (c) onto 100-130 parts by weight of ferroferric oxide powder;

(d) drying the product obtained in the step (c) at the temperature of 80-90 ℃, then heating to 110-;

(e) according to the weight ratio of 5-8:4-5:3-4, stirring and mixing tetrahydrofuran, ferroferric oxide and phosphotungstic heteropoly acid at a low speed at 40-50 ℃, standing until the system is layered after mixing is finished, and taking the lower fluidized part to obtain the phosphotungstic heteropoly acid compounded with the ferroferric oxide magnetic powder.

Preferably, in step 2) and step 3), a constant magnetic field is applied to facilitate the separation of the catalyst when the catalyst is centrifugally separated.

Preferably, in the step 3), the extracting agent is n-octane, and the extraction temperature is 58-63 ℃.

Preferably, in the step 4), the adsorbent is 20-40 mesh silica gel or coconut shell activated carbon. The refining temperature of the refiner is 155-165 ℃.

The polytetramethylene ether glycol is prepared by a polytetramethylene ether glycol production line, as shown in fig. 1, the polytetramethylene ether glycol production line comprises an intensified disperser 1, a main reaction kettle 2, a primary centrifuge 3, a first distillation tower 4, a secondary centrifuge 5, an adsorption column 6, a second distillation tower 7, a settling separator 8 and a static device 9 which are sequentially connected. The reinforced disperser consists of a static mixing section 15, a distribution plate 16 and a circulating heat exchange section 17 from bottom to top in sequence.

Preferably, a catalyst return pipeline 10 which returns to the static mixing section is arranged at the bottom of the main reaction kettle, the primary centrifugal machine and the secondary centrifugal machine. And tetrahydrofuran reflux pipelines 11 which reflux to the static mixing section are arranged at the tops of the first distillation tower and the second distillation tower.

Preferably, as shown in FIG. 3, the distribution plate is provided with through holes 12 having a diameter of 0.5 to 1 mm. As shown in fig. 2, the static mixing section is composed of horizontal SV type mixing units 13 (3) and vertical SV type mixing units 14 (2) arranged at intervals.