CN115724821A - Preparation method and device of lactide - Google Patents

Abstract

The invention provides a preparation method and a device of lactide, wherein the preparation method of the lactide comprises the following steps: carrying out condensation reaction on lactic acid subjected to oligomerization reaction under the catalysis of a metal catalyst under the protection of inert gas crushed by micro bubbles to form condensation polymer, and carrying out repeated recrystallization on the condensation polymer by adopting a composite reagent to obtain lactide; the metal catalyst is a dual-active metal catalyst taking alumina and polysilane as dual carriers, and the active metal is at least two of yttrium, lanthanum, chromium, zinc and nickel. According to the invention, the aluminum oxide and the polysilane are selected as double carriers to prepare the metal catalyst to catalyze the oligomerization reaction, so that the reaction rate is increased, and meanwhile, the composite reagent is used for repeated recrystallization, so that the purity of the lactide is increased.

Description

Preparation method and device of lactide

Technical Field

The invention relates to the field of lactide preparation, in particular to a method and a device for preparing lactide.

Background

Lactide is an organic compound, is a colorless transparent sheet or needle crystal, is easily soluble in chloroform and ethanol, and is insoluble in water. Easy hydrolysis and polymerization, and can be preserved at low temperature.

The production, development and utilization of lactide are more and more emphasized in recent years, because the ring-opening polymerization of lactide is an effective method for preparing high-molecular-weight polylactic acid, and polylactic acid is an environment-friendly material, has good physical properties, biocompatibility and degradation performance, and can be used as a degradation material of plastics and a biodegradable medical suture, and the ring-opening polymerization reaction of lactide is an effective method for preparing high-molecular-weight polylactic acid, and the molecular weight of the polymerization product polylactic acid can reach millions.

The existing preparation process of lactide comprises the following steps:

(1) Oligomerization reaction: the lactic acid is subjected to multistage esterification reaction under certain temperature and pressure conditions, and is dehydrated and polycondensed into oligomer;

(2) And (3) synthesis reaction: the oligomer is thermally decomposed under certain temperature and pressure conditions to break chains to form lactide.

The oligomerization reaction is a reversible reaction, the reaction materials can be diluted by the presence of water, the reaction rate is influenced, and the normal proceeding of the reaction process is further influenced, and the synthesis reaction has the advantages that the system viscosity is large, the separation interface is small, the generated lactide cannot be taken out in time, so that the esterification reaction is balanced, the oligomer is caused to proceed toward the polymerization reaction direction, the lactide product purity is reduced, the retention time in the reaction process is long, the number of byproducts is large, and the product purity is also influenced.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The first object of the present invention is to provide a method for preparing lactide, which increases the reaction rate by catalyzing the oligomerization reaction with a metal catalyst, and increases the purity of lactide by re-crystallizing the polycondensate with a complex reagent.

The second purpose of the present invention is to provide an apparatus for preparing lactide, which is based on a microbubble pulverization technology, wherein the vaporized material and inert gas are pulverized into micron-sized bubbles by a microbubble pulverizer, and the micron-sized bubbles are dispersed into a solution to form a microbubble system, such that a reaction temperature can be reduced, and a reaction efficiency can be improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a preparation method of lactide, which comprises the following steps:

carrying out condensation reaction on lactic acid subjected to oligomerization reaction under the catalysis of a metal catalyst under the protection of inert gas crushed by micro bubbles to form a condensation polymer, and carrying out repeated recrystallization on the condensation polymer by adopting a composite reagent to obtain lactide. In the invention, the oligomerization reaction is catalyzed by adopting a metal catalyst, the use efficiency of the lactic acid is improved, and meanwhile, the polycondensate is recrystallized for multiple times by adopting a composite reagent, so that the purity of the lactide is ensured.

Preferably, the metal catalyst is a dual-active metal catalyst taking alumina and polysilane as dual carriers, and the active metal is at least two of yttrium, lanthanum, chromium, zinc and nickel.

Preferably, the mass ratio of the active metal to the carrier is (2-3): 1.

preferably, the mass ratio of the active metal to the support is 2:1.

in the invention, alumina and polysilane are selected as catalyst carriers, because the alumina is an oxide consisting of two elements of metal elements and oxygen elements, and is used as a carrier, the particles can be prevented from sintering at high temperature after the synthesis of the metal catalyst, the catalytic activity of the catalyst metal can be improved, the cost is reduced, and meanwhile, stable nano particles can be provided, and a high specific surface, an oxygen donor and an acid site donor are constructed; polysilanes, also known as organometallic compounds, are compounds containing one or more metal-carbon bonds in the molecule and are polymeric materials with a backbone composed of silicon atoms. Because of the low electronegativity of Si and the 3d hollow orbit, electrons can be delocalized widely along the main chain of Si, so that polysilane has some characteristics of photoconduction, three-order nonlinear optics, photoluminescence, electroluminescence and the like, the polysilane is combined with active metal, and metal organic groups can be grafted on the surface of the active metal to prepare inorganic-organic hybrid materials with definite surface composition and structure and special performance, surface metal clusters, surface functionalized membranes and the like.

Preferably, the mass ratio of the aluminum oxide to the polysilane is 1: (1-5);

preferably, the mass ratio of the aluminum oxide to the polysilane is 1:3;

preferably, the metal catalyst is yttrium and lanthanum bimetallic catalyst taking alumina and polysilane as double carriers.

Preferably, the polysilane has a weight average molecular weight of 500 to 1000.

Preferably, the polysilane has a weight average molecular weight of 800.

Preferably, the mass ratio between yttrium and lanthanum is (1-3): 1.

preferably, the mass ratio between yttrium and lanthanum is 1:1.

in the present invention, the polysilane used is a polymer having an electronic characteristic derived from sigma-conjugated electrons of a silicon skeleton, which have a reducing ability to generate metal nano-ions from a metal salt, and can stabilize the metal nano-ions by multiple weak interactions, and alumina as a stabilizer can stabilize the structure of the catalyst, and in the metal reduction process, part of Si-Si bonds are converted into Si-O-Si bonds, and thus partial cross-linking of siloxane and alumina proceeds through hydrogen bonds, which is very important for the stability of the catalyst and the prevention of metal leaching. When both are used as a carrier at a certain mass ratio, the advantages of both can be fully utilized, and the stability of the catalyst can be improved.

In the invention, yttrium and lanthanum are selected as metal catalysts, the yttrium and the lanthanum are rare earth elements, and after the yttrium and the lanthanum are matched with alumina and organic matters for use, the surface structure of the yttrium and the lanthanum can be obviously changed, the coordination state of surface cations and oxygen ions and the number and the types of surface composite active centers can be changed, the phase microstructure can be changed, the structural defect memory can be increased, the electronic state can be changed, and the catalytic activity can be obviously increased.

Preferably, the preparation method of the metal catalyst comprises the following steps:

under the atmosphere of inert gas, crushing aluminum oxide, mixing the crushed aluminum oxide with polysilane to form a mixture, heating the mixture to 30-50 ℃, and changing the inert gas into water vapor for activation;

mixing at least two active metal salt solutions with the mixture, soaking for 2-4h, calcining at 100-200 ℃, washing with deionized water, and drying to obtain a solid;

stirring and mixing a modifier and deionized water to obtain an impregnation liquid, putting a solid into the impregnation liquid, heating to 200-400 ℃ at a speed of 10-15 ℃/min in an inert gas atmosphere in a water bath at 10-100 ℃, and keeping for 20-50min;

cooling to room temperature, soaking in the crude salt solution for 2-3h, washing with deionized water, and drying to obtain a metal catalyst;

preferably, the active metal salt solution is formed by mixing a yttrium chloride solution and a lanthanum nitrate solution;

preferably, the mass percentage concentration of the yttrium chloride solution is more than 50%;

preferably, the mass percentage concentration of the lanthanum nitrate solution is more than 60 percent

Preferably, the mixing and soaking time of the active metal salt solution and the mixture is 3 hours;

preferably, the modifier is one or two of diphenyl methane phosphine, potassium permanganate, hydrogen peroxide and nitric acid;

preferably, the modifier is a mixture of 1: (1-5) mixing diphenyl methane phosphine and potassium permanganate;

preferably, the modifier is a mixture of 1:2.8 of diphenyl phosphine and potassium permanganate.

In the invention, the surface of the catalyst carrier can be modified by selecting the diphenyl methane phosphine and the potassium permanganate as the modifying agent, the adsorbability of the catalyst carrier to active metal is increased, and the quantity of the active metal on the catalyst carrier is increased, so that the catalytic activity of the prepared catalyst is increased, and the diphenyl methane phosphine and the potassium permanganate have low cost and wide sources and are easy for large-scale production. And practice shows that the mass ratio of the modifier to the modifier is controlled in a proper range, so that the adsorption performance of the carrier is optimal, and the active ingredients of the catalyst are well adsorbed, so that the catalytic activity is optimal.

Preferably, the temperature of the water bath is 80 ℃, the temperature is increased to 315 ℃ at the speed of 13 ℃/min, and the temperature is maintained for 33min;

preferably, the time for immersion in the crude salt solution is 2.5h;

preferably, the inert gas is ammonia gas.

Preferably, the complex reagent comprises an alcohol complex reagent, an ester complex reagent and a ketone complex reagent.

The alcohol compound reagent is selected as the reagent for recrystallization, because the solubility of the alcohol substance changes obviously along with the temperature, the alcohol substance can be refluxed at higher temperature to dissolve more compound substances, and can be removed easily after the recrystallization is finished; the ester compound reagent is selected because the ester compound reagent is a polar reagent with quite strong dissolving capacity, and the ketone compound reagent can increase the vapor pressure of the mixed solution to ensure that the ketone compound reagent volatilizes more quickly.

The alcohol composite reagent comprises 10-20wt% of ethylene glycol monobutyl ether, 20-30wt% of ethylene glycol, 5-10wt% of diethylene glycol, 3-5wt% of n-propanol and the balance of ethanol;

the ester composite reagent comprises 30-40wt% of ethyl acetate, 20-40wt% of dimethyl carbonate and the balance of ethylene carbonate;

the ketone complex reagent comprises 20-40wt% of N-methylpyrrolidone, 10-20wt% of cyclohexanone, 10-20wt% of butanone, and the balance of acetone.

Preferably, the alcohol complex reagent comprises 15wt% of butyl glycol, 18wt% of ethylene glycol, 6wt% of diethylene glycol, 4wt% of n-propanol, 57wt% of ethanol;

the ester composite reagent comprises 38wt% of ethyl acetate, 30wt% of dimethyl carbonate and 32wt% of ethylene carbonate;

the ketone complex reagent comprises 32wt% of N-methylpyrrolidone, 18wt% of cyclohexanone, 12wt% of butanone and 38wt% of acetone.

The purity of the lactide can be obviously improved by adopting the composite reagent for recrystallization, and the effect of removing impurities is achieved.

Preferably, the recrystallization comprises the steps of:

and recrystallizing the polycondensate for 1-2 times by adopting a ketone compound reagent, recrystallizing the polycondensate for 2-3 times by adopting an ester compound reagent, and finally recrystallizing the polycondensate for 3-5 times by adopting an alcohol compound reagent.

Preferably, the ketone compound reagent is recrystallized at 20-30 ℃, the ester compound reagent is recrystallized at 50-80 ℃, and the alcohol compound reagent is recrystallized at 150-200 ℃;

preferably, the ketone complex reagent is recrystallized at 27 ℃, the ester complex reagent is recrystallized at 70 ℃, and the alcohol complex reagent is recrystallized at 172 ℃.

Preferably, the recrystallization comprises the steps of:

the polycondensate was recrystallized 2 times with a ketone complex reagent, 2 times with an ester complex reagent, and 4 times with an alcohol complex reagent.

According to the invention, firstly, the ketone composite reagent is adopted because the ketone composite reagent can increase the vapor pressure and accelerate the evaporation speed of the polycondensate, then the ester composite reagent is adopted, the dissolving power of the ester composite reagent is adopted to further remove substances in the polycondensate, and finally the alcohol composite reagent is finally treated, because the alcohol composite reagent can dissolve more substances at a higher temperature, meanwhile, the alcohol composite reagent can be well cleaned, and can be conveniently and quickly cleaned after the recrystallization is finished, so that the purity of the lactide after the recrystallization is ensured. The selection of the components and the proportion of the composite reagent is finally determined on the basis of fully considering the purification effect of lactide, and the specific ketone composite reagent and the ester composite reagent can achieve good purification effect.

The invention also provides a device used in the preparation method of the lactide, which comprises a recrystallization tank for recrystallization, and a microbubble grinder is added in the oligomerization reaction and the condensation reaction.

Compared with the prior art, the invention has at least the following advantages:

(1) Firstly, the invention adopts the combination of alumina and polysilane as the dual carrier to prepare the metal catalyst taking active metal as the bimetal, thereby greatly improving the catalytic performance and stability of the metal catalyst, simultaneously reducing the consumption of the cocatalyst and saving resources.

(2) The invention adopts the diphenyl methane phosphine and the potassium permanganate to carry out surface modification on the metal catalyst, thereby increasing the catalytic performance.

(3) The invention adopts the alcohol compound reagent, the ester compound reagent and the ketone compound reagent to carry out repeated recrystallization, thereby improving the purity of the lactide.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are conventional products which are not indicated by manufacturers and are commercially available.

Example 1

The embodiment provides a device for preparing lactide, which comprises an oligomerization reaction tower and a condensation reaction tower which are communicated.

The external microbubble rubbing crusher group that has on the oligomerization tower, microbubble rubbing crusher group includes two external microbubble crushers that communicate through the pipeline for with the broken dispersion of gaseous phase material for the microbubble and carry the oligomerization tower through the pipeline and react.

A microbubble crusher is also arranged in the condensation reaction tower and is used for crushing the inert gas into microbubbles.

Crude lactide generated by condensation reaction sequentially enters a recrystallization tank through a pipeline, a composite reagent is placed in the recrystallization tank and used for recrystallizing the crude lactide, and the treated lactide is sent to a lactide storage tank for storage after passing through a lactide flaker.

In this embodiment, the preparation method of lactide includes the following steps:

(1) Preparation of metal catalysts

(1) Preparing a carrier: under the atmosphere of ammonia gas, 1.5g of alumina is selected to be ground and then mixed with 4.5g of polysilane (with the weight-average molecular weight of 800) to form a mixture, and then the mixture is heated to 40 ℃, and simultaneously, the ammonia gas is replaced by steam to be activated;

(2) dipping: mixing a 50% yttrium chloride solution and a 60% lanthanum nitrate solution to form a mixed solution, mixing the mixed solution and the mixed solution, then dipping at room temperature, wherein the dipping time is 3h, calcining at 180 ℃ after the dipping is finished, washing with deionized water, and drying to obtain a solid, wherein the mass ratio of yttrium to lanthanum in the solid is 1:1, the mass ratio of the total mass of the two active metals to the carrier is 2:1;

(3) modification: selecting a solution formed by mixing 1.0g of diphenyl methyl phosphine and 2.8g of potassium permanganate as a modifier, adding the modifier into deionized water, stirring to obtain an impregnation solution, putting the dried solid into the impregnation solution, carrying out water bath at 80 ℃, then heating at a speed of 13 ℃/min in an ammonia atmosphere, and keeping for 30min after heating to 315 ℃;

(4) and (3) drying: and standing, cooling to room temperature, taking out the solid, putting the solid into a crude salt solution, soaking for 2.5 hours, washing with deionized water, and drying to obtain the metal catalyst.

(2) Preparation of crude lactide

And (2) introducing 200g of lactic acid in the raw material tank into an oligomerization reaction tower, carrying out oligomerization reaction by taking the prepared metal catalyst as a catalyst (5 g), and rectifying the generated oligomer in a first lactide rectifier and a second lactide rectifier to obtain a polycondensate, namely crude lactide (165 g).

(3) Recrystallization of crude lactide

The crude lactide obtained was recrystallized 2 times at 27 ℃ in a first recrystallization tank filled with a ketone complex reagent (250 g) consisting of 32wt% of N-methylpyrrolidone, 18wt% of cyclohexanone, 12wt% of butanone, 38wt% of acetone.

And then the mixture enters a second recrystallization tank to be recrystallized for 2 times at the temperature of 70 ℃, and an ester compound reagent (250 g) is arranged in the second recrystallization tank and is formed by mixing 38wt% of ethyl acetate, 30wt% of dimethyl carbonate and 32wt% of ethylene carbonate.

And finally, recrystallizing for 4 times in a third recrystallization tank at the temperature of 172 ℃, wherein the third recrystallization tank is provided with an alcohol composite reagent (300 g), and the alcohol composite reagent is formed by mixing 15wt% of ethylene glycol butyl ether, 18wt% of ethylene glycol, 6wt% of diethylene glycol, 4wt% of n-propanol and 57wt% of ethanol.

The recrystallized lactide (160 g) was passed through a lactide flaking machine and sent to a lactide storage tank for storage, and the yield of lactide obtained was 98wt%.

The lactide product was tested to have a content of 99.9wt% L-lactide and a content of meso-lactide (endo-lactide) of 0.1wt%.

Examples 2 to 4

The specific embodiment is identical to example 1, except as indicated in table 1 below:

TABLE 1 influence of the Metal catalyst on the yield of lactide

Example 5

The specific implementation manner is the same as that in example 1, the only difference is that the selected active metal salt solution is a mixture of 50% by mass of zinc acetate and 50% by mass of yttrium chloride, the yield of the obtained lactide is 94wt%, and the content of L-lactide is 99.6wt%.

Examples 6 to 8

The specific embodiment is identical to example 1, except as indicated in table 2 below:

TABLE 2 influence of the conditions for preparing the catalyst on the yield of lactide

Examples 9 to 10

The specific embodiment is identical to example 1, except as indicated in table 3 below:

TABLE 3 Effect of modifiers on lactide yield

Example 11

The specific embodiment corresponds to example 1 with the only difference that the modifier is chosen to be hydrogen peroxide, resulting in a lactide yield of 96wt% and an L-lactide content of 99.7wt%.

Example 12

The specific embodiment corresponds to example 1, with the only difference that the modifier is selected to be a mixture of 1.0g of hydrogen peroxide and 2.8g of potassium permanganate, resulting in a lactide yield of 94wt% and an L-lactide content of 99.6wt%

Example 13

The specific implementation is the same as example 1, with the only difference that the modifier is selected to be 1.0g of diphenyl phosphine mixed with 8.0g of potassium permanganate, the yield of lactide obtained is 93wt%, and the content of L-lactide is 99.5wt%

Examples 14 to 15

The specific embodiment is identical to example 1, except as indicated in table 4 below:

TABLE 4 influence of alcohol complexing agent on L-lactide content

Examples 16 to 17

The specific embodiment is identical to example 1, except as indicated in table 5 below:

TABLE 5 influence of ester complexing agents on the content of L-lactide

Examples 18 to 19

The specific embodiment is identical to example 1, except as indicated in table 6 below:

TABLE 6 influence of Ketone Complex reagents on the content of L-lactide

Example 20

The specific implementation manner is the same as that of example 1, and the only difference is that the mass ratio of the aluminum oxide to the polysilane is 5:1, the yield of the obtained lactide was 95wt%, and the content of L-lactide was 99.5wt%.

Example 21

The specific implementation manner is the same as that of example 1, and the only difference is that the mass ratio of the aluminum oxide to the polysilane is 1:8, the yield of the obtained lactide was 89wt%, and the content of L-lactide was 99.6wt%.

Example 22

The specific embodiment is identical to example 1, with the only difference that recrystallization was not carried out using an alcohol complexing agent, resulting in a lactide yield of 94wt% and a L-lactide content of 98.7wt%.

Example 23

The specific implementation manner is the same as that of example 1, and the only difference is that the alcohol complex reagent, the ketone complex reagent and the ester complex reagent are used for recrystallization in sequence, the yield of the obtained lactide is 95wt%, and the content of the obtained L-lactide is 98.3wt%.

Example 24

The specific embodiment corresponds to example 1 with the only difference that no modifier is used, the yield of lactide obtained is 90/wt% and the content of L-lactide obtained is 98.5wt%.

Examples 25 to 29

The specific embodiment is identical to example 1, except as indicated in table 7 below:

TABLE 7 Effect of Metal salt solutions on the yield of lactide

It can be known from the experimental data analysis of the above examples 1 to 29 that the yield of lactide obtained by preparing lactide according to the scheme of the present invention is more than 90wt%, wherein the content of L-lactide in the product after recrystallization is more than 98.0wt%, in examples 9 to 13 of the present invention, the ratio of the modifier is changed, it is found that, after modification with the modifier, the dibenzylphosphine and potassium permanganate can have better modification effect and can better increase the catalytic effect of the catalyst, and after the hydrogen peroxide and potassium permanganate are used for matching, the catalytic effect is lower than that of example 1 of the present invention, but the reason may be that the two properties are similar and the effect of very strongly changing the binding force of the carrier surface is not achieved, and when excessive potassium permanganate is used, the excessive potassium permanganate can react with a part of metal ions to affect the adsorption effect of the metal ions, so that the amount of the modifier is controlled to be in a proper range.

First, in example 20, the increase in the amount of alumina was not achieved well, because the stability of alumina in example 20 stabilized the catalyst sufficiently, and even if the amount of alumina is increased, the stability did not increase, which resulted in a great waste, while in example 21, the stability and activity of the catalyst were found to decrease significantly, which resulted in incomplete oligomerization and excessive impurities in the final product, which resulted in a decrease in the yield of lactide. In examples 22 and 23, after the modification of the composite reagents for recrystallization, since the alcohol composite reagents were not used or the order of use of the alcohol composite reagents was changed, some of the remaining reagents for recrystallization could not be cleaned up well during the recrystallization, resulting in a reduction in the content of L-lactide in the final product. It can be seen from the data of example 24 that the catalytic effect of the metal catalyst is significantly reduced after the metal catalyst is modified without using the modifier, because the adsorption property is reduced without modifying the surface of the metal catalyst, which results in a reduction in the amount of active metal bound to the carrier, and thus results in a catalytic effect inferior to that of example 1.

From the data of examples 25 to 29, it can be seen that when the amounts of the active metal salt solution and the mix are changed, the data of example 27 shows that when the amount of the active metal is too small, the amount of the active metal adsorbed to the carrier is small, and the catalytic effect is not as good as that of example 1, and the yield of lactide is too low, whereas from the data of example 28 shows that when the impregnation time of the mixed solution and the mix is too short, the active metal is not sufficiently adsorbed to the carrier, and the catalytic effect is not as good as that of example 1, and from the experimental data of example 29, when the amount of the active metal is too large, the active metal is adsorbed to the carrier, and aggregated, and the catalytic effect is affected.

It is understood that the amounts and order of use of the reagents in the present invention are critical, and that excellent lactide can be produced only by strictly following the protocol of the present invention.

Finally, it is to be understood that the above embodiments are merely exemplary embodiments employed to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention, and these changes and modifications are to be considered as within the scope of the invention.

Claims (9)

1. A method for preparing lactide is characterized by comprising the following steps:

carrying out condensation reaction on lactic acid subjected to oligomerization reaction under the catalysis of a metal catalyst under the protection of an inert gas crushed by micro bubbles to form a condensation polymer, and carrying out repeated recrystallization on the condensation polymer by adopting a composite reagent to obtain lactide;

the metal catalyst is a dual-active metal catalyst taking alumina and polysilane as dual carriers, and the active metal is at least two of yttrium, lanthanum, chromium, zinc and nickel;

preferably, the mass ratio of the active metal to the carrier is (2-3): 1;

preferably, the mass ratio of the active metal to the carrier is 2:1.

2. the method according to claim 1, wherein the mass ratio of the aluminum oxide to the polysilane is 1: (1-5);

preferably, the mass ratio of the aluminum oxide to the polysilane is 1:3;

preferably, the polysilane has a weight average molecular weight of 500 to 1000;

preferably, the polysilane has a weight average molecular weight of 800;

preferably, the metal catalyst is an yttrium and lanthanum bimetallic catalyst taking alumina and polysilane as double carriers;

preferably, the mass ratio between yttrium and lanthanum is (1-3): 1;

preferably, the mass ratio between yttrium and lanthanum is 1:1.

3. the method according to claim 1, wherein the method for preparing the metal catalyst comprises the steps of:

under the atmosphere of inert gas, crushing aluminum oxide, mixing the crushed aluminum oxide with polysilane to form a mixture, heating the mixture to 30-50 ℃, and changing the inert gas into water vapor for activation;

mixing at least two active metal salt solutions with the mixture, soaking for 2-4h, calcining at 100-200 ℃, washing with deionized water, and drying to obtain a solid;

stirring and mixing a modifier and deionized water to obtain an impregnation liquid, putting a solid into the impregnation liquid, heating to 200-400 ℃ at a speed of 10-15 ℃/min in an inert gas atmosphere in a water bath at 10-100 ℃, and keeping for 20-50min;

cooling to room temperature, soaking in the crude salt solution for 2-3h, washing with deionized water, and drying to obtain a metal catalyst;

preferably, the active metal salt solution is formed by mixing a yttrium chloride solution and a lanthanum nitrate solution;

preferably, the mass percentage concentration of the yttrium chloride solution is more than 50%;

preferably, the mass percentage concentration of the lanthanum nitrate solution is more than 60%;

preferably, the mixing and soaking time of the active metal salt solution and the mixture is 3h;

preferably, the modifier is one or two of diphenyl methane phosphine, potassium permanganate, hydrogen peroxide and nitric acid;

preferably, the modifier is a mixture of 1: (1-5) mixing the diphenyl methane phosphine with potassium permanganate;

preferably, the modifier is a mixture of 1:2.8 of diphenyl phosphine and potassium permanganate;

preferably, the temperature of the water bath is 80 ℃, the temperature is increased to 315 ℃ at the speed of 13 ℃/min, and the temperature is maintained for 33min;

preferably, the time for immersion in the crude salt solution is 2.5h;

preferably, the inert gas is ammonia.

4. The preparation method of claim 1, wherein the complex reagent comprises an alcohol complex reagent, an ester complex reagent and a ketone complex reagent;

the alcohol composite reagent comprises 10-20wt% of ethylene glycol monobutyl ether, 20-30wt% of ethylene glycol, 5-10wt% of diethylene glycol, 3-5wt% of n-propanol and the balance of ethanol;

the ester composite reagent comprises 30-40wt% of ethyl acetate, 20-40wt% of dimethyl carbonate and the balance of ethylene carbonate;

the ketone complex reagent comprises 20-40wt% of N-methyl pyrrolidone, 10-20wt% of cyclohexanone, 10-20wt% of butanone and the balance of acetone.

5. The preparation method according to claim 4, wherein the alcohol complex reagent comprises 15wt% butyl cellosolve, 18wt% ethylene glycol, 6wt% diethylene glycol, 4wt% n-propanol, 57wt% ethanol;

the ester composite reagent comprises 38wt% of ethyl acetate, 30wt% of dimethyl carbonate and 32wt% of ethylene carbonate;

the ketone complex reagent comprises 32wt% of N-methylpyrrolidone, 18wt% of cyclohexanone, 12wt% of butanone, 38wt% of acetone.

6. The method according to claim 4, wherein the recrystallization comprises the steps of:

and recrystallizing the polycondensate for 1-2 times by adopting a ketone compound reagent, recrystallizing the polycondensate for 2-3 times by adopting an ester compound reagent, and finally recrystallizing the polycondensate for 3-5 times by adopting an alcohol compound reagent.

7. The preparation method of claim 6, wherein the ketone complex reagent is recrystallized at 20-30 ℃, the ester complex reagent is recrystallized at 50-80 ℃, and the alcohol complex reagent is recrystallized at 150-200 ℃;

preferably, the ketone complex reagent is recrystallized at 27 ℃, the ester complex reagent is recrystallized at 70 ℃, and the alcohol complex reagent is recrystallized at 172 ℃.

8. The method of claim 5, wherein the recrystallization comprises the steps of:

the polycondensate was recrystallized 2 times with a ketone complex reagent, 2 times with an ester complex reagent, and 4 times with an alcohol complex reagent.

9. The apparatus for use in the production method according to any one of claims 1 to 8, characterized by comprising a recrystallization tank for performing recrystallization, and a microbubble pulverizer is added during the oligomerization reaction and the condensation reaction.