阅读说明：本技术 一种乙交酯的制备方法 (Preparation method of glycolide ) 是由 孙红影 李进 王炳春 王贤彬 于 2020-10-16 设计创作，主要内容包括：本发明提供一种乙交酯的制备方法。所述乙交酯的制备方法是将气态的乙醇酸酯在含钛分子筛催化的条件下,进行环化反应,得到产品乙交酯。本发明提供的制备方法反应条件温和,产品收率高,可连续化进行,不需要高真空和高沸点溶剂的参与。(The invention provides a preparation method of glycolide. The preparation method of the glycolide comprises the step of carrying out cyclization reaction on gaseous glycolate under the catalysis of a titanium-containing molecular sieve to obtain the product glycolide. The preparation method provided by the invention has the advantages of mild reaction conditions, high product yield, continuous operation and no need of high vacuum and high boiling point solvent.)

1. The preparation method of glycolide is characterized in that gaseous glycolic acid ester is subjected to cyclization reaction under the condition of catalysis of a titanium-containing molecular sieve to obtain the product glycolide.

2. The method of claim 1, wherein the titanium-containing molecular sieve is a titanium-containing molecular sieve of a regular structure.

3. The method of claim 1 or 2, wherein the titanium-containing molecular sieve is one or a combination of two or more of TS-1, Ti-MWW, Ti-MOR, Ti-Beta, Ti-ZSM-22, and Ti-ZSM-35,

preferably, the titanium-containing molecular sieve is one or the combination of more than two of TS-1, Ti-MWW and Ti-MOR.

4. The method of any one of claims 1-3, wherein the titanium-containing molecular sieve has a crystallinity of greater than 95%;

alternatively, preferably, the titanium-containing molecular sieve has a grain size of 100-3000nm, more preferably 150-1500 nm.

5. The method of any one of claims 1 to 4, wherein the titanium-containing molecular sieve has a microporous or hierarchical pore structure.

6. The method according to any one of claims 1 to 5, wherein the titanium dioxide content of the titanium-containing molecular sieve is 0.1 wt% to 10 wt%, preferably 1 wt% to 5 wt%.

7. The production method according to any one of claims 1 to 6, wherein the glycolic acid ester is one or a combination of two or more of methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate, preferably one or two of methyl glycolate and ethyl glycolate.

8. The production method according to any one of claims 1 to 7, characterized in that the glycolic acid ester is vaporized into a gaseous state under heating;

preferably, the vaporization temperature is 150-.

9. The method according to any one of claims 1 to 8, wherein the cyclization reaction temperature is 240-320 ℃, preferably 250-300 ℃;

preferably, the reaction pressure is normal pressure;

preferably, the mass space velocity of the feed is from 0.5 to 5g of glycolate per gram of catalyst per hour.

10. The process according to any one of claims 1 to 9, wherein the cyclization reaction is carried out in a fixed bed, a fluidized bed, a moving bed, an ebullating bed or an expanded bed.

11. The titanium-containing molecular sieve is applied to the preparation of glycolide.

Technical Field

The invention belongs to the field of catalytic reaction, and particularly relates to a preparation method of glycolide.

Background

Environmental pollution (i.e., "white contamination") caused by uncontrolled mass production of non-degradable petroleum-based plastics and abuse of disposable petroleum-based plastic articles has attracted serious worldwide attention. Biodegradable polymers based on renewable raw materials have gained many important applications in the biomedical field, such as controlled release drug carriers, absorbable surgical sutures, implantable hard tissue repair materials, etc., and can be used as environmentally friendly materials for manufacturing agricultural films, packaging materials, disposable hygiene products, disposable catering products, etc.

Polyglycolic acid (PGA) is the simplest-structured linear aliphatic polyester and the earliest commercialized in vivo absorbable polymer material. Due to excellent biodegradability and tissue compatibility, the material is widely applied to the fields of absorbable sutures, suture reinforcement materials, fracture fixation materials, drug controlled release systems, tissue engineering scaffold materials and the like. In principle, glycolic acid can be produced by a direct polycondensation method, but it is difficult to produce a polymer having a relatively high molecular weight by the direct polycondensation method, and polyglycolic acid having a high molecular weight can be synthesized from glycolide.

At present, most mature and most applied glycolide synthesis methods at home and abroad mainly adopt a polycondensation-depolymerization method using glycolic acid as a raw material, which is adopted by Dupont, Wu Yue chemical company in Japan and the like, but the method has harsh reaction conditions, needs to be carried out in the presence of a high-temperature, high-vacuum and high-boiling-point solvent, most of catalysts are tin-containing inorganic compounds, and the catalysts cannot be recycled after being used, so that large-scale industrial production is limited. Patent CN1266146C discloses a glycolide production method, in which glycolic acid oligomer and polar high-boiling-point organic solvent (boiling point 230-450 ℃) are reacted under the conditions of 0.1-90KPa and 230-320 ℃, and glycolide is collected in the form of reaction distillate.

Aiming at the current development situation of the coal chemical industry in China, the advantages of the existing glycol technology and the device capacity are fully utilized to develop low-cost methyl glycolate derivative products and application, and in recent years, the synthesis method of glycolide by taking methyl glycolate as a raw material is reported, but the synthesis method is still a polycondensation-depolymerization method, the catalyst is still not recyclable, and the problems of harsh glycolide synthesis conditions and catalyst recycling are not fundamentally solved.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for preparing glycolide with high conversion rate and high selectivity.

The preparation method of the glycolide provided by the invention takes the titanium-containing molecular sieve as the catalyst, and the glycolide is continuously synthesized by a one-step method under the gas phase and normal pressure, so that the synthesis process of the glycolide is simplified.

The invention provides a preparation method of glycolide, which comprises the step of carrying out cyclization reaction on gaseous glycolate under the condition of catalysis of a titanium-containing molecular sieve to obtain the product glycolide.

The preparation method provided by the invention uses glycollic acid ester as a raw material and a titanium-containing molecular sieve as a catalyst to synthesize glycolide by a gas-phase normal-pressure one-step method.

Preferably, the titanium-containing molecular sieve is a titanium-containing molecular sieve with a regular structure.

The titanium-containing molecular sieve with a regular structure in the invention is a titanium-containing molecular sieve with higher crystallinity and regular appearance.

Preferably, the titanium-containing molecular sieve is one or a mixture of more of TS-1, Ti-MWW, Ti-MOR, Ti-Beta, Ti-ZSM-22 and Ti-ZSM-35.

More preferably, the titanium-containing molecular sieve is one or the combination of more than two of TS-1, Ti-MWW and Ti-MOR.

Preferably, the titanium-containing molecular sieve has a crystallinity of greater than 95%.

Preferably, the titanium-containing molecular sieve has a grain size of 100-3000nm, preferably 150-1500 nm.

Preferably, the titanium-containing molecular sieve is of a microporous or hierarchical pore structure.

Preferably, the titanium dioxide content in the titanium-containing molecular sieve is 0.1 wt% to 10 wt%, preferably 1 wt% to 5 wt%.

Preferably, the glycolic acid ester is one or a combination of two or more of methyl glycolate, ethyl glycolate, propyl glycolate and butyl glycolate, and preferably one or two of methyl glycolate and ethyl glycolate.

Preferably, the glycolic acid ester vaporization temperature is 150-600 ℃, more preferably 200-400 ℃.

Preferably, the cyclization reaction temperature is 240-320 ℃, more preferably 250-300 ℃.

Preferably, the reaction pressure is atmospheric.

Preferably, the feed mass space velocity is from 0.5 to 5g glycolate per gram of catalyst per hour, more preferably, the feed mass space velocity is from 1 to 3g glycolate per gram of catalyst per hour.

Preferably, the catalyst and the raw material are subjected to gas phase contact reaction.

Preferably, the cyclization reaction is carried out in a fixed bed, a fluidized bed, a moving bed, an ebullating bed or an expanded bed.

The glycolide is prepared by a bulk polymerization method under the action of a tin-containing catalyst, wherein the relative weight average molecular weight of the glycolide is more than 1 x 10⁵The polyglycolic acid contains stannous octoate or stannous chloride as a tin catalyst.

The preparation method of the polyglycolic acid has the polymerization temperature of 150-.

Compared with the traditional synthesis method of firstly carrying out polycondensation and then carrying out depolymerization, the method has the advantages of mild reaction conditions, high product yield, high conversion rate of glycolate and high selectivity of glycolide. The method can be continuously carried out, high vacuum and high boiling point solvents are not needed, compared with the conventional metal compound catalyst, the catalyst used in the method is safe, environment-friendly and recyclable, and the method is more suitable for industrial production of glycolide.

Drawings

FIG. 1 is an XRD spectrum of the titanium silicalite TS-1 of example 1;

FIG. 2 is an XRD spectrum of the Ti-MWW titanium silicalite molecular sieve of example 2;

FIG. 3 is an XRD spectrum of the titanium containing molecular sieve Ti-MOR of example 3;

FIG. 4 is an XRD spectrum of the titanium containing molecular sieve Ti-Beta of example 4;

FIG. 5 is the FI-IR spectrum of glycolide synthesized in example 6;

FIG. 6 is a 1H NMR spectrum of glycolide synthesized in example 6.

Detailed Description

The invention is illustrated by the following specific examples. Unless otherwise specified, all technical means used in the present invention are well known to those skilled in the art. In addition, the embodiments should be considered illustrative, and not restrictive, of the scope of the invention, which is defined solely by the claims. It will be apparent to those skilled in the art that various changes or modifications in the components and amounts of the materials used in these embodiments can be made without departing from the spirit and scope of the invention.

The invention provides a preparation method of glycolide.

In a specific embodiment provided by the invention, the preparation method of glycolide performs cyclization reaction on gaseous glycolate under the condition of catalysis of a titanium-containing molecular sieve to obtain the product glycolide.

The reaction formula for synthesizing glycolide by cyclizing glycollate is as follows:

r can be methyl, ethyl, n-propyl, isopropyl or n-butyl.

In a specific embodiment provided by the present invention, the titanium-containing molecular sieve is a titanium-containing molecular sieve with a regular structure.

The titanium-containing molecular sieve with a regular structure in the invention is a titanium-containing molecular sieve with higher crystallinity and regular appearance.

In a specific embodiment provided by the invention, the titanium-containing molecular sieve is one or a mixture of more of TS-1, Ti-MWW, Ti-MOR, Ti-Beta, Ti-ZSM-22 and Ti-ZSM-35.

In a specific embodiment provided by the invention, the titanium-containing molecular sieve is one or a combination of more than two of TS-1, Ti-MWW and Ti-MOR.

In one embodiment of the present invention, the titanium-containing molecular sieve has a crystallinity of greater than 95%.

In a specific embodiment provided by the present invention, the grain size of the titanium-containing molecular sieve is 100-3000nm, preferably 150-1500 nm.

In a specific embodiment provided by the present invention, the titanium-containing molecular sieve is of a microporous or hierarchical pore structure.

In a specific embodiment provided by the present invention, the content of titanium dioxide in the titanium-containing molecular sieve is 0.1 wt% to 10 wt%, preferably 1 wt% to 5 wt%.

In one embodiment of the present invention, the glycolic acid ester is one or a combination of two or more of methyl glycolate, ethyl glycolate, propyl glycolate, and butyl glycolate, and preferably one or two of methyl glycolate and ethyl glycolate.

In a specific embodiment provided by the invention, the vaporization temperature of the glycolic acid ester is 150-.

In one embodiment of the present invention, the cyclization reaction temperature is 240-320 ℃.

In one embodiment of the present invention, the cyclization reaction temperature is 250-300 ℃.

In one embodiment of the present invention, the reaction pressure is atmospheric pressure.

In one embodiment of the present invention, the feed mass space velocity is 0.5 to 5g of glycolate per gram of catalyst per hour.

In one embodiment of the present invention, the feed mass space velocity is 1-3g glycolate/hr per gram catalyst.

In one embodiment, the catalyst and the raw material are subjected to gas-phase contact reaction.

In one embodiment of the present invention, the cyclization reaction is carried out in a fixed bed, a fluidized bed, a moving bed, an ebullating bed or an expanded bed.

In a specific embodiment provided by the present invention, the titanium-containing molecular sieve is used in the preparation of glycolide.

The content of titanium dioxide in the catalyst was measured by an X-ray fluorescence spectrometer (X' AXIOSmAX, Pa.).

Catalyst XRD characterization by X-ray diffraction Analyzer (Pasnake, X' Pert)³Powder) was measured.

The glycolate is selected from any commercially available reagent, and the purity is required to be not less than 98%; the titanium-containing molecular sieve of the catalyst is selected from self-made or commercial molecular sieves, and the relative crystallinity of the titanium-containing molecular sieve is more than 95 percent.

For better illustration of the present invention, the preparation of the titanium-containing molecular sieve is set forth, but is not limited to the titanium-containing molecular sieve prepared by the following method.

The synthesis method of the titanium silicalite TS-1 comprises the following steps: taking silica sol as a silicon source, tetrabutyl titanate as a titanium source and tetrapropyl ammonium bromide as a template agent, crystallizing at the temperature of 150 ℃ and 200 ℃ for 12-48h, and filtering, washing, drying and roasting to obtain the titanium-silicon molecular sieve TS-1 raw powder. And (2) uniformly mixing the raw powder and sesbania powder, adding silica sol, further uniformly mixing, extruding and molding by using a bar extruding machine, drying the molded sample at 100 ℃ for 12 hours, and roasting to obtain the strip-shaped titanium silicalite TS-1.

The synthesis method of the titanium-silicon molecular sieve Ti-MWW comprises the following steps: using boric acid as a boron source, silica sol as a silicon source and piperidine as a template agent, crystallizing at 90-100 ℃ for 24-48h, filtering, washing and drying to obtain B-MWW, carrying out acid treatment and boron removal on the B-MWW, then carrying out secondary hydrothermal crystallization by using tetrabutyl titanate as a titanium source, crystallizing at 150-180 ℃ for 48-72h, filtering, washing, drying and roasting to obtain raw powder of the Ti-MWW molecular sieve, uniformly mixing the raw powder and sesbania powder, adding the silica sol, further uniformly mixing, extruding and molding by using an extruding machine, drying the molded sample at 100 ℃ for 12h, and roasting to obtain the strip Ti-MWW molecular sieve.

The synthesis method of the titanium-containing molecular sieves Ti-MOR, Ti-Beta, Ti-ZSM-22 and Ti-ZSM-35 comprises the following steps: the method comprises the steps of taking MOR, Beta, ZSM-22 and ZSM-35 as carriers, carrying out acid treatment, taking titanium tetrachloride as a titanium source, carrying out gas phase treatment at the temperature of 400 ℃ and 600 ℃ for 6-24h, washing, drying and roasting to obtain raw powder of the titanium-containing molecular sieve, uniformly mixing the raw powder and the sesbania powder, adding a binder, further uniformly mixing, extruding the mixture by using an extruder for molding, drying the molded sample at the temperature of 100 ℃ for 12h, and roasting to obtain the strip-shaped titanium-containing molecular sieve.

The synthetic reaction indexes of glycolide are conversion rate of glycolic acid ester (X) and selectivity of glycolide (S)_GO) Methyl glycolate Linear oligomer Selectivity (S)_n). Linear oligomers refer to dimers and trimers produced by the polymerization of methyl glycolate. The calculation method of each reaction index is as follows:

glycolate conversion X ═ moles of glycolate reacted/total moles of glycolate 100%;

glycolide selectivity S_GOThe moles of glycolide produced by the reaction/(moles of glycolic acid ester reacted/2) × 100%;

methyl glycolate linear oligomer selectivity ═ moles of dimer formed by reaction/(moles of glycolate reacted/2) × 100% + moles of trimer formed by reaction/(moles of glycolate reacted/3) × 100%.

EXAMPLE 1 preparation of titanium silicalite TS-1

Taking silica sol (the content of silica is 30 wt%) as a silicon source, tetrabutyl titanate as a titanium source, tetrapropyl ammonium bromide as a template agent, wherein the mass ratio of the silica sol to the tetrabutyl titanate to the tetrapropyl ammonium bromide is 91.5: 4:4.5, crystallizing at 180 ℃ for 30h, filtering, washing, drying and roasting to obtain the raw powder of the titanium silicalite TS-1. And uniformly mixing 100g of raw powder and 2g of sesbania powder, adding 38g of silica sol, further uniformly mixing, extruding and molding by using a strip extruding machine, drying a molded sample at 100 ℃ for 12h, and roasting to obtain the strip-shaped titanium silicalite molecular sieve TS-1.

The XRD spectrum of the titanium silicalite TS-1 is shown in figure 1, and the crystallinity is 99%.

Example 2 preparation of titanium silicalite Ti-MWW

Boric acid is used as a boron source, silica sol (the content of silicon dioxide is 30 wt%) is used as a silicon source, piperidine is used as a template agent, the mass ratio of boric acid to silica sol to piperidine is 20:53:27, the boric acid to silica sol to piperidine is crystallized for 30h at 100 ℃, B-MWW is obtained after filtering, washing and drying, the B-MWW is treated by nitric acid with the mass fraction of 33% at 120 ℃ for boron removal, tetrabutyl titanate is used as a titanium source for secondary hydrothermal crystallization, crystallization is carried out for 60h at 160 ℃, titanium silicalite Ti-MWW raw powder is obtained through filtering, washing, drying and roasting, 38g of raw powder and 2g of sesbania powder are uniformly mixed, 38g of silica sol is added for further uniform mixing, strip extrusion molding is carried out by a strip extrusion machine, and the molded sample is dried for 12h at 100 ℃ and then roasted to obtain the strip-shaped titanium silicalite molecular sieve Ti-MWW.

The XRD spectrum of the Ti-MWW titanium silicalite molecular sieve is shown in figure 2, and the crystallinity is 98%.

EXAMPLE 3 preparation of titanium containing molecular sieves Ti-MOR

Treating MOR as carrier with 30% nitric acid at a solid-to-liquid ratio of 10:1 at 100 deg.C for 24 hr, filtering, washing, and oven drying. Titanium tetrachloride is used as a titanium source, gas phase treatment is carried out for 12 hours at 500 ℃, raw powder of a titanium-containing molecular sieve is obtained through washing, drying and roasting, 100g of the raw powder and 2g of sesbania powder are uniformly mixed, 30g of silica sol is added, the mixture is further uniformly mixed and then extruded into strips by a strip extruding machine for forming, and the formed samples are dried for 12 hours at 100 ℃ and then roasted to obtain the strip-shaped titanium-containing molecular sieve.

The XRD spectrum of the titanium-containing molecular sieve Ti-MOR is shown in figure 3, and the crystallinity is 96%.

EXAMPLE 4 preparation of titanium containing molecular sieves Ti-Beta

Treating Beta as a carrier by 20% nitric acid, then treating the carrier at a solid-to-liquid ratio of 10:1 at 100 ℃ for 48 hours, then filtering, using titanium tetrachloride as a titanium source, carrying out gas phase treatment at 500 ℃ for 15 hours, washing, drying and roasting to obtain raw powder of a titanium-containing molecular sieve, uniformly mixing 100g of the raw powder and 2g of sesbania powder, adding 38g of silica sol, further uniformly mixing, extruding the mixture by a strip extruding machine for molding, drying the molded sample at 100 ℃ for 12 hours, and then roasting to obtain the strip-shaped titanium-containing molecular sieve.

The XRD spectrum of the titanium-containing molecular sieve Ti-Beta is shown in figure 4, and the crystallinity is 95%.

Example 5

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 220 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 6

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1. Separating and purifying the obtained material to obtain glycolide, and the FI-IR spectrogram and 1H NMR spectrogram of the product are shown in figures 5 and 6 respectively.

Example 7

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 300 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 8

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 250 ℃, the feeding amount of methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 9

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 310 ℃, the feeding amount of methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.

Example 10

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 4g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 11

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 16g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 12

The titanium silicalite molecular sieve Ti-MWW (titanium dioxide content is 3.1 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled into the two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.

Example 13

The titanium-containing molecular sieve Ti-MOR (titanium dioxide content is 3.3 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in Table 1.

Example 14

The titanium-containing molecular sieve Ti-Beta (titanium dioxide content is 2.7 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Example 15

The titanium silicalite TS-1 (titanium dioxide content is 2.9 wt%) catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled at two ends of the reaction tube, the vaporization temperature of ethyl glycolate is 300 ℃, the reaction temperature is 300 ℃, the feeding amount of methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Comparative example 1

Preparing a catalyst: preparing TiO by an isometric impregnation method by using micro silica gel powder or white carbon black as a carrier and tetrabutyl titanate dissolved in isopropanol as a titanium source₂/SiO₂Catalyst, with a titanium dioxide content of 3 wt.%.

Reaction: adding TiO into the mixture₂/SiO₂The catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled into the two ends of the reaction tube, the vaporization temperature of methyl glycolate is 260 ℃, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

Comparative example 2

Preparing a catalyst: preparing TiO by an isometric impregnation method by using micro silica gel powder or white carbon black as a carrier and tetrabutyl titanate dissolved in isopropanol as a titanium source₂/SiO₂Catalyst, with a titanium dioxide content of 3 wt.%.

Reaction: adding TiO into the mixture₂/SiO₂The catalyst is sieved into particles of 20-40 meshes, 4g of the catalyst is filled into the middle section of a fixed bed reaction tube, inert quartz sand is filled into two ends of the reaction tube, methyl glycolate is gasified in a nitrogen atmosphere and then enters the reaction tube together, the gasification temperature is 260 ℃, the volume fraction of the methyl glycolate is 8 percent in a mixed gas of nitrogen and methyl glycolate, the reaction temperature is 280 ℃, the feeding amount of the methyl glycolate is 8g/h, the reaction is carried out under normal pressure, and the reaction result is shown in table 1.

The glycolate conversion, glycolide selectivity and linear oligomer selectivity in the glycolide preparation process provided in examples 5-15 and comparative examples 1 and 2 are shown in table 1 below.

TABLE 1 results of the reaction

As can be seen from Table 1, in examples 5-15, the titanium silicalite molecular sieve is used as the catalyst to catalyze the reaction of glycolate to glycolide, compared with comparative examples 1 and 2, in which TiO is used₂/SiO₂The catalyst can be used for catalyzing the glycolic acid ester reaction to generate glycolide, and the conversion rate of glycolic acid ester, the selectivity of glycolide and the selectivity of linear oligomer are all remarkably improved. Different titanium-containing catalysts were shown to affect glycolate conversion, glycolide selectivity, and linear oligomer selectivity during the glycolate reaction to glycolide. Meanwhile, the glycolic acid ester conversion rate, glycolide selectivity and linear oligomer selectivity are also affected by mixing nitrogen with gasified glycolic acid ester during the reaction process.

Comparative example 6 and comparative example 1. TiO in comparative example 1₂/SiO₂The titanium dioxide content in the catalyst is 3 wt%, while the titanium dioxide content of the titanium silicalite TS-1 in example 6 is 2.9 wt%, which is lower than that in comparative example 1. The conversion of glycolate in comparative example 1 was 46.5%, the glycolide selectivity was 71.3%, and the linear oligomer selectivity was 15.3%. The glycolate conversion was 99.4%, the glycolide selectivity was 93.1%, and the linear oligomer selectivity was 5.0% in example 6, and the glycolate conversion, the glycolide selectivity, and the linear oligomer selectivity were all higher in example 6 than in comparative example 1.

Comparative example 6 and comparative example 2. Comparative example 2 TiO with a titanium dioxide content of 3 wt%₂/SiO₂The catalyst catalyzes glycolic acid ester to react to generate glycolide, and the glycolic acid ester is gasified in nitrogen atmosphere and then enters the reaction tube together, the conversion rate of glycolic acid ester after reaction is 38.4%, the selectivity of glycolide is 90.1%, the selectivity of linear oligomer is 9.0%, and the reaction indexes are all lower than those of the reaction in embodiment 6 of the invention.

Example 16

Preparing polylactic acid: dissolving 0.009g stannous octoate in petroleum ether, adding into a stainless steel reaction kettle together with 30g glycolide, evacuating the kettle with nitrogen gas for at least three times, vacuumizing for 0.5h under stirring to remove petroleum ether, stopping stirring, pressurizing to 1MPa with nitrogen gas, heating to 180 deg.C, starting stirring, timing, and reacting for 3hThen, the reaction was stopped to obtain polyglycolic acid having a relative weight average molecular weight of 1.53X 10 as measured by Gel Permeation Chromatography (GPC)⁵。

The above-mentioned embodiments are only for illustrating the technical idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.