阅读说明：本技术 结晶多孔聚合物材料限域催化丙交酯的合成方法 (Synthetic method of crystalline porous polymer material confined catalytic lactide ) 是由 赵英杰 郭光明 赵劲宇 于 2021-09-15 设计创作，主要内容包括：本发明公开了一种结晶多孔聚合物材料限域催化丙交酯的合成方法,所述方法包括以下步骤：(Ⅰ)合成催化剂；(Ⅱ)限域催化丙交酯的合成；(Ⅲ)提纯丙交酯。本发明结晶聚合物催化L-乳酸合成L-丙交酯产率达到85.6％,产率比现有文献上报道的H-β分子筛催化的产率高出10％；结晶多孔聚合物材料催化剂,易于制备,对环境友好,产率高,易于回收,且连续七次催化产率保持在70％以上,催化产率保持度远高于现有文献报道的催化剂催化效果。(The invention discloses a method for synthesizing lactide by a crystalline porous polymer material in a limited-domain catalysis manner, which comprises the following steps: synthesizing a catalyst; (II) synthesizing lactide by limited-domain catalysis; and (III) purifying the lactide. The yield of the L-lactide synthesized by catalyzing L-lactic acid by the crystalline polymer reaches 85.6 percent, and is 10 percent higher than that of the H-beta molecular sieve catalysis reported in the existing literature; the crystalline porous polymer material catalyst is easy to prepare, environment-friendly, high in yield and easy to recover, the catalytic yield is kept above 70% for seven continuous times, and the catalytic yield retention degree is far higher than the catalytic effect of the catalyst reported in the existing literature.)

1. A method for synthesizing lactide by confined catalysis of a crystalline porous polymer material is characterized by comprising the following steps: the method comprises the following steps:

(I) Synthesis catalyst

Putting the compound A, the compound B, mesitylene and 1, 4-dioxane into a reaction container, uniformly mixing, adding acetic acid, degassing, carrying out vacuum sealing, placing in a drying oven for drying, filtering out precipitates after drying, washing by a Soxhlet extractor, and carrying out vacuum drying after washing to obtain a solid catalyst;

the structural formula of the compound A is as follows:

wherein R is₁＝OH，CH₃，OCH₃，C₂H₅，F，Cl，Br，I；

The structural formula of the compound B is as follows:

wherein R is₂＝COOH，CH₃，OCH₃，C₂H₅，F，Cl，Br，I；

(II) Synthesis of lactide by Domain-restricted catalysis

Adding the catalyst, the solvent and the lactic acid obtained in the step (I) into a reaction vessel for reaction, slowly cooling after the reaction is finished, filtering, washing, and removing the solvent at low pressure to obtain crude lactide;

(III) purification of lactide

And (3) carrying out liquid-liquid extraction on the crude lactide obtained in the step (II) by using toluene and water, taking an organic phase, and removing the solvent at low pressure to obtain the L-lactide.

2. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the structural formula of the compound A is

The structural formula of the compound B is

3. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the molar ratio of the compound A to the compound B in the step (I) is 4: 7; the volume ratio of the mesitylene, the 1, 4-dioxane and the acetic acid is 15:5: 1; the molar ratio of the compound A to mesitylene is 1: 25.

4. the method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the degassing method in the step (I) is a freezing and thawing pump circulation method.

5. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the drying condition of the oven in the step (I) is 80 ℃ for 3 days; the Soxhlet extractor washing specifically comprises the following steps: washing with THF and acetone for 4 hr; the vacuum drying condition is 80 ℃ and 12 hours.

6. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the lactic acid in the step (II) is 90 wt% of L-lactic acid.

7. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the solvent in the step (II) is toluene or o-xylene.

8. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the mass ratio of the catalyst to the lactic acid is 1:10, and the mass-volume ratio of the catalyst to the solvent is 1: 1.

9. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: the reaction conditions of the step (II) are as follows: the reaction time is 5h, and the reaction temperature is 120 ℃.

10. The method for the confined catalytic synthesis of lactide from a crystalline porous polymer material according to claim 1, wherein: and (3) washing in the step (II) by adopting acetonitrile.

Technical Field

The invention belongs to the field of lactide preparation processes, and particularly relates to a synthesis method of lactide through domain-limited catalysis of a crystalline porous polymer material.

Background

Polylactic acid (PLA) is the major synthetic bio-based plastic on the market and has a very wide range of applications. The PLA product can sufficiently replace the current fossil-based plastic product, and the waste thereof can be completely biodegraded in a short period of time, so that it has good environmental performance in life cycle evaluation.

The monomer material for synthesizing the polylactic acid comprises lactic acid and lactide, wherein the lactide is a cyclic dimer of the lactic acid, the chemical synthesis method of the polylactic acid comprises a lactide ring-opening polymerization method (also called a two-step method) and a lactic acid direct polycondensation method, and the two-step method comprises the following process flows: lactic acid, a catalyst → atmospheric distillation → reduced pressure distillation → crude lactide → lactide purification → ring opening polymerization → post treatment → polylactic acid product, the polylactic acid product with higher relative molecular mass can be obtained by the two-step method, but the addition of the reaction step makes the process route more complicated than the one-step method and the intermediate lactide is easy to absorb water.

At present, the two-step method is adopted for preparing lactide industrially, lactic acid is firstly dehydrated and condensed to form lactic acid oligomer, then the oligomer is catalytically cracked at high temperature to obtain the lactide, and the lactide is produced mainly by using a metal salt catalyst, mainly a zinc or tin compound. The whole preparation process needs to be carried out under the conditions of high temperature, negative pressure and catalysis, during the preparation process, in order to improve the overall yield, unreacted substances need to be refluxed and recycled, and finally, qualified lactide products are obtained by a certain purification means. The lactide production process mainly comprises several units of polycondensation, depolymerization and cyclization and purification. The lactide production uses mainly metal salt catalysts, mainly compounds of zinc or tin.

The lactide is prepared by the traditional industrial two-step method, the yield is low, the amount of generated oligomers is large, the preparation factors are influenced a lot, the purification is difficult, and finally the cost is overhigh. The used metal catalyst is easy to pollute products, may pollute the environment, is not in accordance with the environmental protection concept, has low yield and the like.

The existing lactide production process mainly adopts metal catalysts, mainly zinc and tin compounds, such as zinc oxide, stannous octoate, stannous chloride and the like, and the research team of Nanjing university finds that organic guanidine catalysts and alkali metal catalysts can also be used for the production of lactide and polylactic acid. However, the currently used catalysts still have several problems:

(1) because part of the catalyst is powdery solid, the catalyst is difficult to be completely dissolved with lactic acid and is difficult to be directly added into a vacuum system, and the yield of the lactide is finally influenced;

(2) the metal catalyst is easy to form residues in lactide, is not beneficial to the concept of green environmental protection, and the metal residue quantity must be strictly controlled.

(3) The organic guanidine catalyst does not contain metal elements and is a green catalyst with great development potential in the future, but the catalyst is not widely used in the world, and the chemical performance and the economical efficiency of the catalyst are still to be further verified in engineering amplification experiments.

Lactide is the key to the two-step process for preparing polylactic acid, because the purity of lactide determines the molecular length and the use value of the ring-opening polymerization of lactide into polylactic acid. Conventional methods for purifying lactide are mainly recrystallization. Lactide used for manufacturing surgical sutures and other relative high molecular weight polymers needs to be recrystallized for four times, the primary recovery rate is only 93.1 percent at most, a large amount of solvent is wasted in the purification process, the solvent is difficult to recover, and the cost is increased, which is the main reason that the cost of the indirect polymerization method is high.

Disclosure of Invention

The invention is provided for overcoming the defects in the prior art, and aims to provide a method for synthesizing lactide by domain-limited catalysis of a crystalline porous polymer material.

The invention is realized by the following technical scheme:

a method for synthesizing lactide by confined catalysis of a crystalline porous polymer material comprises the following steps:

(I) Synthesis catalyst

Putting the compound A, the compound B, mesitylene and 1, 4-dioxane into a reaction container, uniformly mixing, adding acetic acid, degassing, carrying out vacuum sealing, placing in a drying oven for drying, filtering out precipitates after drying, washing by a Soxhlet extractor, and carrying out vacuum drying after washing to obtain a solid catalyst;

the structural formula of the compound A is as follows:

wherein R is₁＝OH，CH₃，OCH₃，C₂H₅，F，Cl，Br，I；

The structural formula of the compound B is as follows:

wherein R is₂＝COOH，CH₃，OCH₃，C₂H₅，F，Cl，Br，I；

(II) Synthesis of lactide by Domain-restricted catalysis

Adding the catalyst, the solvent and the lactic acid obtained in the step (I) into a reaction vessel for reaction, slowly cooling after the reaction is finished, filtering, washing, and removing the solvent at low pressure to obtain crude lactide;

(III) purification of lactide

And (3) carrying out liquid-liquid extraction on the crude lactide obtained in the step (II) by using toluene and water, taking an organic phase, and removing the solvent at low pressure to obtain the L-lactide.

In the technical scheme, the structural formula of the compound A is shown in the specification

The structural formula of the compound B is

In the technical scheme, the molar ratio of the compound A to the compound B in the step (I) is 4: 7; the volume ratio of the mesitylene, the 1, 4-dioxane and the acetic acid is 15:5: 1; the molar ratio of the compound A to mesitylene is 1: 25.

in the above technical solution, the degassing method in the step (i) is a freeze-thaw pump circulation method.

In the technical scheme, the drying condition of the oven in the step (I) is 80 ℃ for 3 days; the Soxhlet extractor washing specifically comprises the following steps: washing with THF and acetone for 4 hr; the vacuum drying condition is 80 ℃ and 12 hours.

In the above technical scheme, the lactic acid in the step (II) is 90 wt% of L-lactic acid.

In the above technical scheme, the solvent in the step (ii) is toluene or o-xylene.

In the technical scheme, the mass ratio of the catalyst to the lactic acid is 1:10, and the mass-volume ratio of the catalyst to the solvent is 1: 1.

In the above technical scheme, the reaction conditions of the step (ii) are as follows: the reaction time is 5h, and the reaction temperature is 120 ℃.

In the technical scheme, acetonitrile is adopted for washing in the step (II).

The invention has the beneficial effects that:

the invention provides a method for synthesizing lactide through the confined catalysis of a crystalline porous polymer material, wherein the yield of L-lactide synthesized by catalyzing L-lactic acid with a crystalline polymer reaches 85.6 percent, and is 10 percent higher than the yield of the catalysis of an H-beta molecular sieve reported in the prior literature; the crystalline porous polymer material catalyst is easy to prepare, environment-friendly, high in yield and easy to recover, the catalytic yield is kept above 70% for seven continuous times, and the catalytic yield retention degree is far higher than the catalytic effect of the catalyst reported in the existing literature.

Drawings

FIG. 1 is nuclear magnetic data of the catalyst of example 1 of the present invention after completion of the catalytic reaction;

FIG. 2 is an XRD data pattern of the catalyst in repeated experiments according to the present invention (A is before the first catalytic reaction experiment, B is after the seventh catalytic reaction experiment);

FIG. 3 is nuclear magnetic data of the catalyst after the first catalytic experiment in a repeat experiment of the present invention;

FIG. 4 is nuclear magnetic data of the catalyst after the second catalytic experiment in the repeat experiment of the present invention;

FIG. 5 is nuclear magnetic data of the catalyst after the third catalytic experiment in the repeat experiment of the present invention;

FIG. 6 is nuclear magnetic data of the catalyst after the fourth catalytic experiment in the repeat experiment of the present invention;

FIG. 7 is nuclear magnetic data of the catalyst after the fifth catalytic experiment in the repeat experiment of the present invention;

FIG. 8 is nuclear magnetic data of the catalyst after the sixth catalytic experiment in the repeat experiment of the present invention;

FIG. 9 is nuclear magnetic data of the catalyst after the seventh catalytic experiment in the repeat experiment of the present invention.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the technical solutions of the present invention are further described below by way of specific embodiments with reference to the drawings of the specification.

Example 1

A method for synthesizing lactide by confined catalysis of a crystalline porous polymer material is characterized by comprising the following steps: the method comprises the following steps:

(I) Synthesis catalyst

Adding 0.6mmol of compound A and 0.9mmol of compound B into a heat-resistant glass tube, adding 4ml of mesitylene and 16ml of 1, 4-dioxane, uniformly mixing the media by ultrasonic treatment, adding 6ml of 3M acetic acid, carrying out freeze-pump-unfreezing three times for degassing, carrying out vacuum sealing, placing in an oven at 80 ℃ for three days, filtering out precipitates, washing with THF and acetone for four hours respectively through a Soxhlet extractor, and carrying out vacuum drying at 80 ℃ overnight to obtain a solid catalyst COF-Z with the yield of 93%;

the structural formula of the compound A is

The structural formula of the compound B is

The reaction equation for catalyst synthesis is:

(II) Synthesis of lactide by Domain-restricted catalysis

A25 ml round bottom flask is added with 10mg of the catalyst COF-Z obtained in the step (I), 100mg of 90 wt% of L-LA and 10ml of toluene or o-xylene, a water separator is added on the flask, a condensing tube is connected on the water separator, the reaction is carried out for 5H, after slow cooling, filtration is carried out, acetonitrile is used for washing, the solvent is removed under low pressure, the yield is calculated by HPLC and 1H-NMR respectively, and the highest yield of the COF-Z-1 catalyst is found to be 85.6%. The nuclear magnetic data of COF-Z-1 after catalytic treatment is shown in FIG. 1.

(III) purification of lactide

Removing solvent under low pressure (obviously separating out many crystals at the bottom of the flask) to obtain crude lactide, liquid-liquid extracting with toluene and water, and removing solvent under low pressure to obtain L-lactide with purity of 98.5%.

The experiment was repeated:

the experiment was repeated using the same experimental conditions as in example 1. The experimental conditions of the repeated experiment are the same as that of example 1, the same catalyst is used in the repeated experiment, the mass of the L-lactic acid used in the experiment is determined according to the mass of the recovered catalyst in order to recover the catalyst from the previous experiment, and the mass of the L-lactic acid is 10 times of the mass of the catalyst, and the specific data are shown in the following table.

As can be seen by the comparison of the experimental data and the graphs 2-9, the COF-Z-1 catalyst is continuously catalyzed for seven times in o-xylene, the yield is still over 70%, the structure is still kept complete through XRD comparison, and the COF-Z-1 catalyst has high stability and repeatability.

The reaction principle of the invention is as follows:

(I) Synthesis catalyst

Because the catalyst COF-Z has a large number of carboxyl and hydroxyl functional groups and can ionize hydrogen ions in toluene and o-xylene, the pore diameter of the COF-Z is about 2.1nm, and the length of L-lactic acid is about 0.4nm, the COF-Z can promote dimer cyclization to form lactide by the ionized hydrogen ions in a selective catalysis mode.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.