CN115501829A

CN115501829A - Device suitable for preparing polyglycolic acid with narrow molecular weight distribution and preparation method thereof

Info

Publication number: CN115501829A
Application number: CN202110691886.9A
Authority: CN
Inventors: 张雄伟; 王赛博; 孙朝阳
Original assignee: Pujing Chemical Industry Co Ltd
Current assignee: Pujing Chemical Industry Co Ltd
Priority date: 2021-06-22
Filing date: 2021-06-22
Publication date: 2022-12-23

Abstract

The invention discloses a device and a method for preparing polyglycolic acid with narrow molecular weight distribution. The device comprises a melting mixing kettle, a static mixer connected with a discharge port of the melting mixing kettle, and tackifying equipment arranged at the downstream of the static mixer.

Description

Device suitable for preparing polyglycolic acid with narrow molecular weight distribution and preparation method thereof

Technical Field

The invention relates to the field of polymer preparation, in particular to a device suitable for preparing polyglycolic acid with narrow molecular weight distribution and a preparation method thereof.

Background

In the modern society, with the rapid advance of the development of polymer science and technology, various polymer materials are also deeply inserted into the daily life of people, so that the choices of clothes, food, live and go of people are greatly enriched, and great convenience is brought to the life of people. However, the polymer material products have more and more wastes after use, which bring great harm to the environment, which also causes the problem of white pollution in social environment to be more and more serious, and the environmental pollution treatment is urgent. In order to solve the problem of white pollution, two main development directions exist at present, namely, research and development of recycling of waste plastics and development of degradable plastics. Because recycling usually has the disadvantages of low recovery rate, serious secondary processing pollution, high labor cost and the like, the development of degradable plastics is the main development trend of the present and even the future.

Polyglycolic acid (also called polyglycolic acid (abbreviated as PGA)) is a biodegradable aliphatic polymer, which can be hydrolyzed under the catalysis of enzymes or acids and bases in microorganisms or organisms to finally form carbon dioxide and water, and is a degradable material with great development potential. In application, because PGA has good biocompatibility, it can be used to produce degradable medical device materials (e.g., absorbable surgical sutures, tissue engineering materials, orthopedic materials, etc.), in addition, because PGA has excellent gas barrier properties, it can also be used in the field of packaging (e.g., shopping bags, express bags, packaging bags, freshness bags, etc.), and further because PGA itself has strong mechanical strength and low environmental load, it can also be used to process into downhole tool members for hydrocarbon resource recovery (e.g., bridge plugs, fracturing balls, etc.), temporary plugging agent materials, etc. Therefore, PGA as a novel degradable material has considerable economic benefits and good application prospects. Based on this, how to produce and process polyglycolic acid product to better replace traditional polymer material has become an important research content.

Researches on a double-screw reactive extrusion process of the PGA material show that the performance difference of the final PGA product is large due to the difference of the length-diameter ratio of the double screws and the difference of the threaded elements; in addition, when the material passing through the twin-screw is in a fluid state, the conveying block, the kneading block and the mixing block can play a good role in mixing and dispersing, but the strong shearing effect of the threaded element is more obvious along with the increase of the molecular weight of the material, so that the material is easily heated unevenly to cause overhigh local temperature, the twin-screw is limited by the sealing condition, and the molecular weight distribution of the material can be in an uneven state under the influence of water and oxygen degradation, so that the molecular weight distribution of the final material is widened and the dispersion coefficient is increased, which can seriously affect the subsequent processing performance of the final material, and the PGA product manufactured by the molding process such as injection molding or blow molding can have obvious defects (for example, the mechanical strength does not reach the standard, the aging resistance is poor, and the normal use of the product is seriously affected; moreover, since PGA itself has a good crystallization ability and a high crystallization speed, when the flow rate of the PGA in the pipe is low, it is easy to crystallize and solidify, and the pipe is blocked, so that the subsequent processing cannot be performed normally.

Therefore, there is a strong need in the art to provide a method for narrowing the molecular weight distribution of the finally obtained polyglycolic acid.

Disclosure of Invention

The present invention aims to provide polyglycolic acid having a narrow molecular weight distribution.

In a first aspect of the present invention, there is provided an apparatus for producing narrow molecular weight distribution polyglycolic acid, comprising a melt-mixing kettle, a static mixer connected to a discharge port of the melt-mixing kettle, and a viscosity-increasing device disposed downstream of the static mixer.

In another embodiment, the apparatus has a reaction aid storage tank connected to the melt mixing kettle feed port.

In another embodiment, the static mixer is connected to the viscosity building equipment via a material transfer assembly.

In another embodiment, the material conveying assembly comprises a material conveying pipeline connecting the discharge port of the static mixer and the feed port of the tackifying device, a melt pump arranged on the material conveying pipeline, and a cleaning liquid drain pipe connected in parallel with the melt pump on the material conveying pipeline.

In another embodiment, a cleaning liquid drainage branch is arranged on a material conveying pipeline between the melt pump and the feed inlet of the tackifying device.

In another embodiment, a three-way valve is arranged at the position where the cleaning solution drain conduit is connected to the material conveying pipeline.

In another embodiment, the cleaning solution drainage branch is connected with the material conveying pipeline through a three-way valve.

In another embodiment, a melt metering pump is arranged between the discharge port of the melting and mixing kettle and the static mixer.

In another embodiment, the apparatus further comprises a falling film evaporation purification unit disposed upstream of and coupled to the melt-mixing kettle.

In another embodiment, the falling film evaporation purification unit comprises a falling film evaporator and a screen, wherein the discharge port at the bottom of the screen is connected with the feed port at the top of the melt mixing kettle.

In another embodiment, a centrifugal washing machine connected to a discharge port of the falling-film evaporator, a vacuum dryer connected to a discharge port of the centrifugal washing machine, and a pulverizer connected to a discharge port of the vacuum dryer are sequentially arranged between the falling-film evaporator and the screener.

In another embodiment, the discharge port of the pulverizer is connected to the feed port of the sifter.

In a second aspect of the present invention, there is provided a process for the preparation of narrow molecular weight distribution polyglycolic acid by the apparatus provided by the present invention as described above, comprising the steps of:

(1) Uniformly mixing glycolide and a reaction auxiliary agent in a melting and mixing kettle to obtain a fluid premix;

(2) Prepolymerizing the fluid premix obtained in step (1) in a static mixer to obtain a glycolic acid prepolymer; and

(3) And (3) subjecting the glycolic acid prepolymer obtained in the step (2) to final polymerization by a tackifying device to obtain polyglycolic acid.

In another embodiment, the purity of the glycolide used in step (1) is 98% or more; preferably not less than 98.5%, and the acidity is not more than 20mmol/kg.

In another embodiment, step (1) uses glycolide powder.

In another embodiment, the reaction auxiliary used in step (1) comprises a catalyst, an initiator and a dehydrating agent.

In another embodiment, the catalyst is used in an amount of 0.001 to 5wt% thereof, the initiator is used in an amount of not more than 5wt% (e.g., without limitation, 0.1 to 4wt%, 1 to 3wt%, etc.), and the dehydrating agent is used in an amount of 0.2 to 1.6wt% thereof, based on the mass of glycolide used in step (1).

In another embodiment, the reaction aid is added dropwise to the melt-mixing kettle in step (1) by injection.

In another embodiment, the static mixer used in step (2) employs at least 2-stage gradient heating.

In another embodiment, the static mixer used in step (2) is a 2-10 stage gradient temperature increasing system, preferably 3-7 stages.

In another embodiment, the first stage temperature ranges between 120-220 ℃; the temperature of the last section is between 220 and 250 ℃.

In another embodiment, the temperature of the second section is increased by between 10-100 ℃ over the temperature of the first section; the temperature of the last section is increased by 0-30 ℃ compared with the temperature of the previous adjacent section.

In another embodiment, the glycolic acid prepolymer obtained in step (2) has a weight average molecular weight of about 5 to 15 ten thousand.

In another embodiment, the tackifying equipment in step (3) is devolatilized at an absolute pressure of less than or equal to 500Pa and at a temperature of between 220 and 250 ℃.

In another embodiment, the screw length to diameter ratio of the devolatilization section may be set to 30 to 100, such as, but not limited to, 40 to 50, 60 to 90, and the like.

In another embodiment, processing aids (e.g., tougheners, compatibilizers, plasticizers, chain extenders, hydrolysis adjustment promoters, hydrolysis adjustment inhibitors, heat stabilizers, antioxidants, antimicrobials, lubricants, etc.) may be added at the beginning of the devolatilization section by weight loss weighing.

In another embodiment, the glycolide of step (1) is obtained by subjecting the molten crude glycolide to evaporation purification by means of a falling-film evaporator.

In another embodiment, the temperature of the falling film evaporator through which the molten crude glycolide passes is less than 200 ℃.

In another embodiment, the pressure in the falling film evaporator does not exceed 5kPa, and the temperature is 5-30 ℃ above the boiling point of glycolide at that pressure.

In another embodiment, the pressure is from 0.4 to 4kPa.

In another embodiment, the temperature is 10-20 ℃ above the boiling point of glycolide at that pressure.

In another embodiment, the falling film evaporator contains n heat exchange devices, n is an integer greater than or equal to 2; the temperature of the n heat exchange devices increases along the flow direction of the molten crude glycolide in a gradient manner.

In another embodiment, n is preferably an integer from 2 to 10.

In another embodiment, the temperature difference between adjacent heat exchange devices is 1-10 ℃; preferably 2-8 deg.C.

In another embodiment, the heat exchanger has an average film thickness of not more than 300. Mu.m.

In another embodiment, the method of subjecting molten crude glycolide to evaporation purification by a falling film evaporator further comprises the steps of: the evaporated and purified material was washed with an alcohol solvent.

Accordingly, the present invention provides a device and a corresponding method for narrowing the molecular weight distribution of polyglycolic acid finally obtained.

Drawings

FIG. 1 is a schematic view of an apparatus for producing narrow molecular weight distribution polyglycolic acid provided in example 1 of the present invention.

FIG. 2 is a schematic view of an apparatus for producing narrow molecular weight distribution polyglycolic acid provided in example 2 of the present invention.

Detailed Description

The inventor finds that the comprehensive energy consumption of the purification process is obviously less than that of the conventional recrystallization purification process by purifying crude glycolide through a falling film evaporator through extensive and intensive research; then, a static mixer is arranged at the upstream of the viscosity increasing device, the static mixer is creatively used as a main place of glycolide polymerization reaction, the mixing effect of glycolide and reaction auxiliary agents is enhanced, meanwhile, the ring-opening polymerization reaction of glycolide is promoted by a multi-stage step temperature increasing mode, glycolic acid prepolymer with higher molecular weight is gradually formed, and the viscosity increasing device mainly plays a role of devolatilization, and residual small molecules in the glycolic acid prepolymer are removed, so that the glycolic acid prepolymer is promoted to be further polymerized, and the molecular weight of the final PGA is increased. On the basis of this, the present invention has been completed.

It should be noted that in the present invention, "tackifying device" plays a role in devolatilization, and can promote further polymerization of glycolic acid prepolymer, and timely remove the generated small molecules, so as to further increase the molecular weight of the polymer, and correspondingly, the viscosity of the polymer; the "tackifying means" in the art may be, for example and without limitation, a twin screw extruder provided with only a devolatilization section.

Preparation device of narrow molecular weight distribution polyglycolic acid

The invention provides a device suitable for preparing narrow molecular weight distribution PGA, which comprises a melt mixing kettle, a static mixer coupled with the melt mixing kettle and a tackifying device arranged at the downstream of the static mixer.

Be equipped with the fuse-element measuring pump between static mixer and the melting mixing kettle, the cauldron bottom discharge gate of melting mixing kettle is connected with static mixer's feed inlet through the fuse-element measuring pump.

And the discharge hole of the static mixer is connected with the feed inlet of the tackifying device through the material conveying component.

The material conveying component comprises a material conveying pipeline for connecting a discharge port of the static mixer with a feed port of the viscosity increasing equipment, a melt pump arranged on the material conveying pipeline, and a cleaning liquid dredging pipeline arranged in parallel with the melt pump, wherein a cleaning liquid discharging branch is arranged on the material conveying pipeline between the melt pump and the feed port of the viscosity increasing equipment.

Preferably, the liquid inlet end and the liquid discharge end of the cleaning liquid dredging pipeline are connected in parallel to two sides of the melt pump through a three-way valve I.

Preferably, the cleaning liquid drainage branch is connected with the material conveying pipeline through a three-way valve II.

Static mixers commonly used in the art, such as, but not limited to, SK type static mixers, SX type static mixers, SV type static mixers, and the like, may be used.

The production device also comprises a falling film evaporation and purification unit which is arranged at the upstream of the melting and mixing kettle and is coupled with the melting and mixing kettle.

The falling film evaporation and purification unit comprises a falling film evaporator, a centrifugal washing machine, a vacuum drier, a crusher and a sieving device, wherein the centrifugal washing machine, the vacuum drier, the crusher and the sieving device are sequentially arranged on the downstream of the falling film evaporator, and a discharge hole in the bottom of the sieving device is connected with a feed inlet in the top of the melting mixing kettle.

Further, the top of the melting mixing kettle is also provided with a reaction material feeding port and a reaction auxiliary agent feeding port, wherein the reaction material feeding port is connected with the weightlessness scale through a material feeding pipe, the reaction auxiliary agent feeding port is connected with a reaction auxiliary agent storage tank arranged at the upstream of the melting mixing kettle through an auxiliary agent feeding pipe, and a liquid metering pump is further arranged on the auxiliary agent feeding pipe between the reaction auxiliary agent storage tank and the reaction auxiliary agent feeding port.

In one embodiment of the invention, the weight loss scale is connected between a discharge port at the bottom of the screen and a reaction material feed port at the top of the melt mixing kettle.

The heat exchange surface of the falling film evaporator is a plurality of sections of heat exchange surfaces with gradually increased temperature from top to bottom and in gradient distribution.

In the technical device, a pipeline, a material conveying pipeline, a cleaning liquid dredging pipeline, a melt metering pump, a melt pump, a three-way valve I and a three-way valve II between a kettle bottom discharge port of a melting mixing kettle and a feed inlet of a static mixer are all provided with conventional heat tracing. In addition, the type of the metering pump can be selected according to the reaction time of materials in the melting mixing kettle and the volume of a pipeline, and the types of the melt pump and the tackifying equipment are matched with the type of the melt metering pump.

As used herein, "coupled" means that two devices are operatively connected in an interactive, interactive relationship with each other.

Preparation method of polyglycolic acid with narrow molecular weight distribution

The invention provides a preparation method of polyglycolic acid with narrow molecular weight distribution, which comprises the following steps:

step one, uniformly mixing glycolide and a reaction auxiliary agent in a melting mixing kettle to obtain a fluid premix;

secondly, conveying the fluid premix into a static mixer for prepolymerization to obtain a glycolic acid prepolymer;

and thirdly, conveying the glycolic acid prepolymer to tackifying equipment for final polymerization to obtain a polyglycolic acid product.

In the first step, the purity of the used glycolide is not less than 98 percent; preferably not less than 98.5%, and acidity not exceeding 20mmol/kg.

In one embodiment of the present invention, glycolide powder is used in the first step.

In an embodiment of the present invention, in the first step, glycolide powder with a purity of not less than 98.5% is introduced into a melt mixing kettle, the temperature is raised to 90-120 ℃ under normal pressure, and a proper amount of reaction auxiliary agent is added while stirring, so that the molten glycolide and the reaction auxiliary agent are uniformly mixed, and a fluid premix is obtained.

The reaction auxiliary agent used in the first step comprises a catalyst, an initiator and a dehydrating agent; in terms of the amount of the reaction aid, the catalyst is used in an amount of about 0.001 to 5wt% based on the mass of the glycolide powder, the initiator is used in an amount of not more than about 5wt% based on the mass of the glycolide powder (for example, but not limited to, 0.1 to 4wt%, 1 to 3wt%, etc.), and the dehydrating agent is used in an amount of about 0.2 to 1.6wt% based on the mass of the glycolide powder.

The catalyst may be selected from at least one of tin-based compounds, antimony-based compounds, or zinc-based compounds, such as, but not limited to, stannous octoate, stannous chloride, tin lactate, antimony trioxide, diethyl zinc, or zinc acetate dihydrate.

The initiator may be selected from one or both of alkane species having a hydroxyl structure such as a primary alcohol or a secondary alcohol (e.g., n-propanol, isopropanol, n-butanol, isobutanol, etc.) or aromatic species having a hydroxyl active group (e.g., benzyl alcohol, phenethyl alcohol, etc.).

The dehydrating agent may be selected from a carbodiimide, a polycarbodiimide, or a carbodiimide-based compound (for example, but not limited to, N' -diisopropylcarbodiimide, dicyclohexylcarbodiimide, etc.).

To prevent local excess concentrations of the reaction aid in molten glycolide, in one embodiment of the invention, the reaction aid may be added dropwise to the melt-mixing kettle by injection.

The static mixer in the second step adopts at least 2-section gradient heating mode, for example, 2-10 section gradient heating mode; preferably, 3 to 7 stages are employed.

In one embodiment of the invention, the first stage temperature of the static mixer ranges from 120 to 220 ℃, such as but not limited to 140-170 ℃, 150-180 ℃, 190-220 ℃ and the like; the final temperature range is 130-250 deg.C, such as but not limited to 150-200 deg.C, 190-230 deg.C, 220-250 deg.C, etc.

In one embodiment of the invention, the second stage of the static mixer is increased in temperature by between 10-100 ℃ over the first stage, such as but not limited to 40-50 ℃, 20-70 ℃, 30-60 ℃, 80-90 ℃ and the like; the last stage is raised from the temperature of the previous adjacent stage by between 0-30 deg.C, such as but not limited to 10-20 deg.C, etc.

In one embodiment of the invention, the static mixer is provided with four sections, wherein the temperature of the first section is set to be 120-180 ℃, the temperature of the second section is set to be 190-210 ℃, the temperature of the third section is set to be 210-220 ℃, and the temperature of the fourth section is set to be 220-230 ℃.

In one embodiment of the invention, the static mixer is provided with five sections, wherein the temperature of the first section is set to be 150-170 ℃, the temperature of the second section is set to be 190-200 ℃, the temperature of the third section is set to be 200-210 ℃, the temperature of the fourth section is set to be 210-220 ℃, and the temperature of the fifth section is set to be 220-230 ℃.

In one embodiment of the invention, the static mixer is provided with three sections, wherein the temperature of the first section is set to be 190-220 ℃, the temperature of the second section is set to be 200-240 ℃, and the temperature of the third section is set to be 220-250 ℃.

In one embodiment of the invention, the total length of time the material is in the static mixer under operating conditions is generally not more than 150 minutes, such as, but not limited to, 60-90 minutes.

The glycolic acid prepolymer obtained in the second step has a weight average molecular weight of about 5 to 15 ten thousand.

In the practical application of the static mixer, if the viscosity of the material in the fluid state between two adjacent sections is too high, a melt pump can be additionally arranged between the two adjacent sections to promote the forward flow of the material.

In the third step, the tackifying equipment is only provided with a devolatilization section, the absolute pressure of the devolatilization section is less than or equal to 500Pa, and the temperature is set to be 220-250 ℃.

Preferably, the screw length to diameter ratio of the devolatilization section is set to 30 to 100, such as, but not limited to, 40 to 50, 60 to 90, and the like.

In the production process, processing aids (e.g., toughening agents, compatibilizers, plasticizers, chain extenders, hydrolysis regulation promoters, hydrolysis regulation inhibitors, heat stabilizers, antioxidants, antibacterial agents, lubricants, etc.) can be added at the beginning of the devolatilization section by weight loss weighing according to actual requirements.

It should be noted that, in the present technology, the tackifying device plays a role in devolatilizing, which can promote further polymerization of the glycolic acid prepolymer, and timely remove the generated small molecules to further increase the molecular weight of the polymer.

In a preferred embodiment of the invention, the temperature of the individual lines is regulated as follows:

the temperature of a pipeline between a discharge port at the bottom of the melt mixing kettle and a feed inlet of the melt metering pump is set to be 90-120 ℃, the temperature of a pipeline between a discharge port of the melt metering pump and a feed inlet of the static mixer is set to be 120-160 ℃, and the temperature of a material conveying pipeline is set to be 220-250 ℃.

In one embodiment of the present invention, the first step further comprises the following steps to obtain the glycolide used in the first step: introducing molten crude glycolide into a falling-film evaporator, performing evaporation purification in vacuum at a temperature 5-30 ℃ (preferably 10-20 ℃) higher than the boiling point of the glycolide corresponding to the vacuum, transferring the obtained material into a centrifugal washing machine, washing, performing centrifugal separation, transferring the solid into a vacuum drier for vacuum drying, crushing the dried solid by a crusher, and sieving by a sieving machine to obtain purified glycolide powder.

As used herein, "crude glycolide" can be a mixture obtained by methods conventional in the art, wherein the glycolide content is less than 98wt% based on the total weight of the mixture, and the mixture also contains heavy end impurities, typically glycolic acid polymers of poor solubility, such as tetramers, pentamers, hexamers of glycolic acid, and light end impurities, typically glycolic acid, water, other acids (such as, but not limited to, methoxyacetic acid in free form, oxalic acid in free form), or residual solvents, and the like.

In one embodiment of the invention, the falling film evaporator comprises n (stages) of heat exchange means, n being an integer of 2 or more, and may be, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

As used herein, the "heat exchange means" may be heat exchange tubes, heat exchange surfaces, or the like.

The molten crude glycolide used in the present invention can be obtained by methods conventional in the art, for example, but not limited to, subjecting the crude glycolide to a temperature of 90 ± 5 ℃ to completely melt it.

In the present invention, the feed rate of crude glycolide to the falling-film evaporator is generally in the range from 300 to 1000 g/h.

The pressure in the falling-film evaporator according to the invention is generally a vacuum, for example an absolute pressure of ≦ 5kPa, preferably 0.4 to 4kPa.

In one embodiment of the invention, the purification temperature in the falling film evaporator is generally less than 200 ℃, preferably not more than 180 ℃, more preferably not more than 160 ℃.

In one embodiment of the invention, the temperatures of the n heat exchange devices in the falling-film evaporator are different and gradually increase along the flow direction of the molten crude glycolide or from top to bottom; the temperature gradient can be that the temperature difference of adjacent heat exchange devices is 1-10 ℃; preferably 2-8 deg.C.

In one embodiment of the invention, when the vacuum in the falling film evaporator is set to be 0.4kPa absolute, the heat exchange surfaces of the falling film evaporator are set to be four sections of heat exchange surfaces, and the temperatures of the sections of heat exchange surfaces are respectively set to be 160 ℃, 164 ℃, 168 ℃ and 170 ℃ from top to bottom.

In one embodiment of the invention, when the vacuum in the falling film evaporator is set to be 1.1kPa absolute, the heat exchange surfaces of the falling film evaporator are set to be five sections of heat exchange surfaces, and the temperatures of the sections of heat exchange surfaces are respectively set to be 170 ℃, 175 ℃, 178 ℃, 182 ℃ and 185 ℃ from top to bottom.

In one embodiment of the invention, when the vacuum in the falling film evaporator is set to be 2.0kPa absolute, the heat exchange surfaces of the falling film evaporator are set to be three sections of heat exchange surfaces, and the temperatures of the sections of heat exchange surfaces are respectively set to be 180 ℃, 186 ℃ and 192 ℃ from top to bottom.

In one embodiment of the invention, when the vacuum in the falling-film evaporator is set to be 3.1kPa absolute, the heat exchange surfaces of the falling-film evaporator are set to be three sections of heat exchange surfaces, and the temperatures of the sections of heat exchange surfaces are respectively set to be 190 ℃, 194 ℃ and 196 ℃ from top to bottom.

In one embodiment of the invention, when the vacuum in the falling film evaporator is set to be 4.1kPa absolute, the heat exchange surfaces of the falling film evaporator are set to be four sections of heat exchange surfaces, and the temperatures of the sections of heat exchange surfaces are respectively set to be 190 ℃, 192 ℃, 195 ℃ and 198 ℃ from top to bottom.

In one embodiment of the invention, when the vacuum in the falling film evaporator is set to be 5.0kPa absolute, the heat exchange surface of the falling film evaporator is set to be two sections of heat exchange surfaces, and the temperature of each section of heat exchange surface is respectively set to be 195 ℃ and 198 ℃ from top to bottom.

In one embodiment of the invention, the average film thickness of the material in the falling-film evaporator from top to bottom along the heat exchange surface of the falling-film evaporator is less than or equal to 300 μm, preferably less than or equal to 120 μm, and more preferably less than or equal to 100 μm.

In one embodiment of the invention, the residence time of the material in the falling-film evaporator on the heat exchange surface is not more than 5min.

The washing in the centrifugal washing machine is generally carried out at normal temperature (10-40 ℃, preferably 20-30 ℃) by using an alcohol solvent; the alcohol solvent includes, but is not limited to, absolute ethanol, methanol, n-propanol, isopropanol, n-butanol, isobutanol, or tert-butanol, etc.

In one embodiment of the present invention, the washing is followed by solid-liquid separation and drying to obtain a purified glycolide product.

Solid-liquid separation can be carried out using methods conventional in the art, such as, but not limited to, filtration, suction filtration, centrifugation, and the like; drying may be carried out using methods conventional in the art, such as, but not limited to, vacuum drying, oven drying, desiccator drying, infrared drying, or the like; in one embodiment of the invention, vacuum drying is used: absolute pressure less than or equal to 500Pa, and drying at 40-60 deg.C for 1-2 hr.

The polyglycolic acid product produced by the process of the present invention has a molecular weight distribution index of about 1.2 to 1.3.

As used herein, "distribution index" is a parameter D representing the width of molecular weight distribution, D = M (w)/M (n), where M (w) is the weight average molecular weight, M (n) is the number average molecular weight, D =1 is a polymer of uniform molecular weight, and the value of D is broader in its molecular weight distribution and greater in the degree of polydispersity as the value of D is greater than 1. The measurement method generally employs Gel Permeation Chromatography (GPC) to measure M (w) and M (n) of a sample, and then calculates the ratio of the two.

The glycolide content of the reaction mass (i.e. the glycolide mass) used in the first step of the process according to the invention can be determined by gas chromatography methods known in the art, and the acidity by potentiometric titration methods known in the art (e.g. by means of an automated potentiometric titrator).

To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.

All features defined herein as numerical ranges or percentage ranges, such as values, amounts, levels and concentrations, are provided for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.

As used herein, the term "about" when used to modify a numerical value means within 5% of the error margin measured for that value.

The features mentioned above with reference to the invention, or the features mentioned with reference to the embodiments, can be combined arbitrarily. All features disclosed in this specification may be combined in any combination, provided that there is no conflict between such features and the combination, and all possible combinations are to be considered within the scope of the present specification. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, the features disclosed are merely generic examples of equivalent or similar features.

The main advantages of the invention are:

1. compared with the conventional recrystallization purification process, the method has the advantages that the crude glycolide is purified by the falling film evaporator without using a solvent, the heavy components in the crude glycolide are removed to the maximum extent on the premise of shortening the evaporation heating time of the glycolide as much as possible to reduce the self-polymerization degree of the glycolide, and the light components (such as glycolic acid, water or free acid) in the crude glycolide can be removed in subsequent washing, namely the use of the falling film evaporator can not only remarkably reduce the usage amount of the solvent, but also greatly reduce the comprehensive energy consumption of the crude glycolide purification process and save the production cost.

2. According to the invention, a melt mixing kettle is coupled with a static mixer, glycolide and a reaction auxiliary agent are fully and uniformly mixed through the melt mixing kettle to obtain a premix, and then the premix is introduced into the static mixer for prepolymerization, so that the premix is creatively and efficiently mixed to play a role in low-shear high-dispersion, heat accumulation in a local area in a material is favorably prevented and eliminated, and side reactions such as thermal degradation and the like caused by uneven heating in the material can be effectively prevented, thereby ensuring that the glycolide can be subjected to good prepolymerization reaction, a glycolic acid prepolymer with a certain molecular weight is obtained, and then the glycolic acid prepolymer is introduced into tackifying equipment (for example, a double-screw extruder only provided with a devolatilization section) for final polymerization, so that the time of the material subjected to high-shear action in the tackifying equipment can be effectively shortened, the occurrence of the thermal degradation side reactions and the like is favorably inhibited, the occurrence of ester exchange reaction is favorably inhibited, the content of low-polymer and/or low-molecular-chain substances in a system is reduced, the molecular weight distribution index can be remarkably improved, and the molecular weight distribution index is more uniform.

3. The invention introduces the fluid premix of the molten glycolide into a static mixer, utilizes a cross flow mode to enhance the mixing effect between the glycolide and the reaction auxiliary agent, enables the reaction auxiliary agent to be more uniformly dispersed in a reaction system, simultaneously utilizes a gradient temperature rising mode to firstly more gently initiate the ring-opening polymerization reaction of the glycolide at a relatively low temperature within a relatively short time, then appropriately raises the temperature and appropriately prolongs the time to form a glycolic acid molecular chain which is relatively stable and has reaction activity in the reaction system, and then further increases the glycolic acid molecular chain at a relatively high temperature and within a relatively long time to obtain the glycolic acid prepolymer with a certain molecular weight.

4. The main polymerization reaction is carried out in the static mixer, and the static mixer reduces the influence of oxygen and moisture on the polymerization reaction to the maximum extent; and the characteristic of good uniform heat transfer effect of the static mixer is utilized, so that the molecular chain in the polymerization reaction can keep stable growth for a longer time, and the local temperature rise of a reaction system caused by the high shearing action in a conventional reaction type double-screw extruder is too fast, so that the side reactions such as thermal degradation and the like can be more easily generated in advance, the molecular weight of a final product is not improved, the molecular weight distribution of the final product is widened, and the processing, the mechanical property and the aging resistance of the material are negatively influenced.

5. The invention is suitable for amplification production, is beneficial to saving the modification cost of the process flow, can realize low-carbonization continuous production, and has outstanding economical practicability.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers. All percentages, ratios, proportions, or parts are by weight unless otherwise specified. The units in weight volume percent in the present invention are well known to those skilled in the art and refer to, for example, the weight (g) of solute in 100ml of solution. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.

In the examples described below, the glycolide content of the purified glycolide powders concerned can be determined by gas chromatography methods known in the art, the glycolide powder particle size being determined by the mesh size of the sieve, for example by using a 70 mesh (corresponding to about 200 μm) sieve or by using a sieve with more than 70 mesh, the glycolide powder being capable of being sieved and having a particle size substantially satisfying "D ₉₀ Less than or equal to 200 μm ", and the acidity is determined by potentiometric titration methods known in the art (for example, by means of an automated potentiometric titrator).

For the test of the molecular weight and the distribution of polyglycolic acid, gel Permeation Chromatography (GPC) method is used for the test, which is as follows:

a0.2 g sample of PGA was dissolved in 100mL of hexafluoroisopropanol solution having a sodium trifluoroacetate content of 5mmol/L, filtered through a polytetrafluoroethylene filter having a pore size of 0.4. Mu.m, and 20. Mu.L of the filtrate was introduced into an "LC-20AD GPC" sample injector manufactured by Shimadzu (Japan) under test conditions: the column temperature is 40 ℃; eluent: hexafluoroisopropanol with 5mmol/L of sodium trifluoroacetate dissolved therein; the flow rate is 1mL/min; a detector: an RI detector; and (3) correction: five different standards of polymethyl methacrylate with molecular weights varying between 7000 and 200000 were used for molecular weight correction.

In the following examples, the volume of the melting and stirring tank used was 50L, the volume of the static mixer was 8L, the maximum delivery flow rate of the melt-metering pump was 10L/h, and the maximum delivery flow rate of the melt pump was 12L/h.

The static mixer used in the following examples was a commercially available SK type static mixer.

Apparatus example 1

Provides a device for preparing polyglycolic acid with narrow molecular weight distribution as shown in figure 1.

Apparatus a for narrow molecular weight distribution PGA included a melt-mixing kettle 100, a static mixer 200 coupled to the melt-mixing kettle, and a viscosity-increasing device 300 (shown in the form of a twin-screw extruder) disposed downstream of the static mixer.

A melt metering pump 120 is arranged between the static mixer and the melting mixing kettle, and a kettle bottom discharge port of the melting mixing kettle 100 is connected with a feed port of the static mixer 200 through the melt metering pump 120.

The outlet of the static mixer 200 is connected with the inlet of the viscosity-increasing device 300 through the material conveying component 230.

The material conveying assembly 230 comprises a material conveying pipeline 231 for connecting the discharge port of the static mixer 200 with the feed port of the tackifying device 300, a melt pump 232 arranged on the material conveying pipeline, and a cleaning solution dredging pipeline 233 arranged in parallel with the melt pump 232, wherein a cleaning solution drainage branch 234 is arranged on the material conveying pipeline 231 between the melt pump 232 and the feed port of the tackifying device 300.

The liquid inlet end and the liquid outlet end of the cleaning liquid dredging pipeline 233 are connected in parallel to both sides of the melt pump 232 through a three-way valve 235-I.

The cleaning solution draining branch 234 is connected with the material conveying pipeline 231 through a three-way valve 235-II.

The top of the melting mixing kettle 100 is provided with a reaction material feeding port and a reaction auxiliary agent feeding port, wherein the reaction material feeding port is connected with a weightlessness scale 1112 through a material feeding pipe 112, the reaction auxiliary agent feeding port is connected with a reaction auxiliary agent storage tank 110 arranged at the upstream of the melting mixing kettle through an auxiliary agent feeding pipe 111, and a liquid metering pump 1111 is further arranged on the feeding pipe 111 between the reaction auxiliary agent storage tank 110 and the reaction auxiliary agent feeding port.

The pipeline between the discharge port at the bottom of the melting and mixing kettle 100 and the feed port of the static mixer 200, the material conveying pipeline 231, the cleaning liquid dredging pipeline 233, the melt metering pump 120, the melt pump 232, the three-way valve 235-I and the three-way valve 235-II are all provided with conventional heat tracing.

Apparatus example 2

An apparatus for producing polyglycolic acid having a narrow molecular weight distribution as shown in FIG. 2 is provided.

Apparatus A' for narrow molecular weight distribution PGA includes a melt-mixing kettle 100, a static mixer 200 coupled to the melt-mixing kettle, and a viscosity-increasing device 300 (shown in the form of a twin-screw extruder) disposed downstream of the static mixer.

The outlet of the static mixer 200 is connected with the inlet of the viscosity increasing device 300 through the material conveying component 230.

The material conveying component 230 comprises a material conveying pipeline 231 for connecting the discharge port of the static mixer 200 with the feed port of the viscosity increasing equipment 300, a melt pump 232 arranged on the material conveying pipeline, and a cleaning solution dredging pipeline 233 arranged in parallel with the melt pump 232, wherein a cleaning solution drainage branch 234 is arranged on the material conveying pipeline 231 between the melt pump 232 and the feed port of the viscosity increasing equipment 300.

The liquid inlet end and the liquid outlet end of the cleaning liquid dredging pipeline 233 are connected in parallel to two sides of the melt pump 232 through a three-way valve 235-I.

Apparatus a' further includes a falling film evaporation purification unit 400 disposed upstream of the melt-mixing kettle 100 and coupled to the melt-mixing kettle 100.

The falling film evaporation purification unit 400 comprises a falling film evaporator 410, a centrifugal washing machine 420, a vacuum drier 430, a pulverizer 440 and a screener 450 which are sequentially arranged below the falling film evaporator, wherein a discharge hole at the bottom of the screener 450 is connected with a feed hole at the top of the melting and mixing kettle 100 through a weightlessness scale 1112.

The top of the melting mixing kettle 100 is provided with a reaction material inlet and a reaction auxiliary agent inlet, wherein the reaction material inlet is connected with a weightlessness scale 1112 through a material inlet pipe 112, the reaction auxiliary agent inlet is connected with a reaction auxiliary agent storage tank 110 arranged at the upstream of the melting mixing kettle through an auxiliary agent inlet pipe 111, and a liquid metering pump 1111 is further arranged on the inlet pipe 111 between the reaction auxiliary agent storage tank 110 and the reaction auxiliary agent inlet.

The heat exchange surface of the falling film evaporator 410 is a plurality of sections of heat exchange surfaces with gradually increased temperature from top to bottom and in gradient distribution.

Preparation of example 1

Introducing molten crude glycolide into a falling-film evaporator (such as a evaporator with a height of 30cm and a bottom diameter of 10 cm) at a feeding rate of 600 g/hr, setting the vacuum in the falling-film evaporator to be about 0.4kPa, setting the heat exchange surfaces of the falling-film evaporator to be four sections of heat exchange surfaces, setting the temperatures of the heat exchange surfaces from top to bottom to be about 160 ℃, about 164 ℃, about 168 ℃ and about 170 ℃, setting the average film-forming thickness of the material from top to bottom along the whole heat exchange surface to be about 92 μm, setting the evaporation retention time of the material on the whole heat exchange surface to be about 68s, transferring the glycolide material after evaporation purification into a centrifugal washing machine, washing, centrifuging, and transferring the solid into a vacuum drying machineVacuum drying (absolute pressure less than or equal to 500Pa, drying at 60 deg.C for 1 hr), pulverizing the dried solid, and sieving to obtain purified glycolide powder (D) ₉₀ Less than or equal to 200 mu m, the purity is more than or equal to 98.5 percent, and the acidity is less than or equal to 20 mmol/kg); introducing the purified glycolide powder into a melt mixing kettle, heating to about 115 ℃ under normal pressure, stirring while adding reaction auxiliary agents (taking the mass of the purified glycolide powder as a reference, the addition of a catalyst (stannous octoate) is about 0.001wt%, the addition of an initiator (isopropanol) is about 0.1wt%, and the addition of a dehydrating agent (dicyclohexylcarbodiimide) is about 0.2 wt%) into the melt mixing kettle in an existing injection mode within about 5min, and continuously stirring and mixing for about 10min to uniformly mix the molten glycolide and the reaction auxiliary agents to obtain a fluid premix; the premix in a fluid state is conveyed into a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (the weight average molecular weight of the glycolic acid prepolymer is about 13.82 ten thousand by GPC measurement after sampling), then the glycolic acid prepolymer is conveyed into tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and the material from the head of the tackifying equipment is subjected to liquid nitrogen quenching to obtain the polyglycolic acid product.

Preparation of example 2

Introducing molten crude glycolide into a falling-film evaporator (for example, 45cm in height and 10cm in bottom diameter) at a feeding rate of 500 g/hr, setting the vacuum in the falling-film evaporator to be about 1.1kPa under the absolute pressure, setting the heat exchange surface of the falling-film evaporator to be five sections of heat exchange surfaces, setting the temperatures of the heat exchange surfaces from top to bottom to be about 170 ℃, 175 ℃, 178 ℃, 182 ℃ and 185 ℃, setting the average film-forming thickness of the material along the whole heat exchange surface from top to bottom to be about 101 μm, setting the evaporation retention time of the material on the whole heat exchange surface to be about 134s, transferring the glycolide material after evaporation purification into a centrifugal washing machine, washing and centrifugally separating, transferring the solid into a vacuum drier for vacuum drying (the absolute pressure is less than or equal to 500Pa and the temperature is less than or equal to 60 ℃ for 1 hour), crushing the dried solid by a crusher, and sieving by a sieve to obtain purified glycolide powder (D) ₉₀ ≤200μmThe purity is more than or equal to 98.5 percent, and the acidity is less than or equal to 20 mmol/kg); introducing the purified glycolide powder into a melt mixing kettle, heating to about 118 ℃ under normal pressure, stirring while adding a reaction auxiliary agent (based on the mass of the purified glycolide powder, the addition of a catalyst (formed by mixing stannous chloride and antimony trioxide in a mass ratio of 1; and (2) conveying the premix in a fluid state into a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (the weight average molecular weight of the glycolic acid prepolymer is about 15.03 ten thousand by GPC measurement after sampling), then conveying the glycolic acid prepolymer into tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and quenching the material discharged from the head of the tackifying equipment by liquid nitrogen to obtain the polyglycolic acid product.

Preparation of example 3

Introducing molten crude glycolide into a falling-film evaporator (for example, with a height of 60cm and a bottom diameter of 20 cm) at a feeding rate of 700 g/hr, setting the vacuum in the falling-film evaporator to be about 2.0kPa, setting the heat exchange surface of the falling-film evaporator to be three heat exchange surfaces, setting the temperatures of the heat exchange surfaces from top to bottom to be about 180 ℃, about 186 ℃ and about 192 ℃, respectively, setting the average film-forming thickness of the material from top to bottom along the whole heat exchange surface to be about 117 μm, setting the evaporation retention time of the material on the whole heat exchange surface to be about 296s, transferring the glycolide material after evaporation purification into a centrifugal washing machine, washing, centrifugally separating, transferring the solid into a vacuum drier for vacuum drying (the absolute pressure is less than or equal to 500Pa, drying is carried out at 40 ℃ for 2 hours), crushing the dried solid by a crusher, sieving by a sieving machine, and obtaining purified glycolide powder (D) ₉₀ Less than or equal to 200 mu m, the purity is more than or equal to 98.5 percent, and the acidity is less than or equal to 20 mmol/kg); the purified glycolide powder was then introduced into a melt-mixing kettle, heated to about 110 ℃ at atmospheric pressure, and passed through the existing kettle while stirringThe injection method of (1) is that a reaction auxiliary agent (taking the mass of purified glycolide powder as a reference, the addition amount of a catalyst (formed by mixing diethyl zinc and tin lactate according to a mass ratio of 1; the premix in a fluid state is conveyed to a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (a sample is taken, and the weight average molecular weight of the glycolic acid prepolymer is about 10.27 ten thousand by GPC measurement), then the glycolic acid prepolymer is conveyed to tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and the material from the head of the tackifying equipment is subjected to liquid nitrogen quenching to obtain a polyglycolic acid product.

Preparation of example 4

Introducing molten crude glycolide into a falling-film evaporator (for example, with the height of 36cm and the diameter of the bottom surface of 8 cm) at a feeding rate of 980 g/h, setting the vacuum in the falling-film evaporator to be about 3.1kPa under the absolute pressure, setting the heat exchange surface of the falling-film evaporator to be three sections of heat exchange surfaces, setting the temperatures of the heat exchange surfaces from top to bottom to be about 190 ℃, about 194 ℃ and about 196 ℃, setting the average film-forming thickness of the material along the whole heat exchange surface from top to bottom to be about 298 [ mu ] m, setting the evaporation retention time of the material on the whole heat exchange surface to be about 129s, controlling the time of the material passing through the heat exchange surface of the falling-film evaporator to be about 40 minutes, setting the film-forming thickness of the material along the heat exchange surface from top to bottom to be less than or equal to 100 [ mu ] m, transferring the glycolide material after evaporation and purification into a centrifugal washing machine, after washing and centrifugal separation, transferring the solid into a vacuum drier for vacuum drying (drying under the absolute pressure of less than or equal to be less than or equal to 500Pa and at 50 ℃ for 2 hours), crushing and sieving the dried solid, thus obtaining purified glycolide powder (D) ₉₀ Less than or equal to 200 mu m, the purity is more than or equal to 98.5 percent, and the acidity is less than or equal to 20 mmol/kg); then purified glycolide powder is introduced into a melt mixing kettle, the temperature is raised to about 120 ℃ under normal pressure, and reaction auxiliary agent is added in about 5min by the existing injection mode while stirringTaking the mass of the purified glycolide powder as a reference, completely adding the catalyst (antimony trioxide) in an amount of about 0.05wt%, the initiator (n-butanol) in an amount of about 0.8wt%, and the dehydrating agent (carbodiimide) in an amount of about 0.3wt% into a melting and mixing kettle, and continuously stirring and mixing for about 10min to uniformly mix the molten glycolide and the reaction auxiliary agent to obtain a fluid premix; and (2) conveying the premix in a fluid state into a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (the weight average molecular weight of the glycolic acid prepolymer is about 8.76 ten thousand by GPC measurement after sampling), then conveying the glycolic acid prepolymer into tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and quenching the material discharged from the head of the tackifying equipment by liquid nitrogen to obtain the polyglycolic acid product.

Preparation of example 5

Introducing molten crude glycolide into a falling-film evaporator (for example, with a height of 20cm and a bottom diameter of 10 cm) at a feeding rate of 300 g/hr, setting the vacuum in the falling-film evaporator to be about 4.1kPa, setting the heat exchange surface of the falling-film evaporator to be four sections of heat exchange surfaces, setting the temperatures of the heat exchange surfaces from top to bottom to be about 190 ℃, about 192 ℃, about 195 ℃ and about 198 ℃, setting the average film-forming thickness of the material from top to bottom along the whole heat exchange surface to be about 53 μm, setting the evaporation retention time of the material on the whole heat exchange surface to be about 52s, transferring the glycolide material after evaporation purification into a centrifugal washing machine, washing, centrifugally separating, transferring the solid into a vacuum drier for vacuum drying (drying at an absolute pressure of 500Pa or less and 60 ℃ for 2 hours), crushing the dried solid by a crusher, and sieving by a sieve, thus obtaining purified glycolide powder (D) ₉₀ Less than or equal to 200 mu m, the purity is more than or equal to 98 percent, and the acidity is less than or equal to 20 mmol/kg); then, the purified glycolide powder was introduced into a melt mixing kettle, the temperature was raised to about 112 ℃ under normal pressure, and while stirring, the reaction aid [ based on the mass of the purified glycolide powder, the amount of the catalyst (stannous octoate, antimony trioxide and zinc acetate dihydrate in a mass ratio of 5Carbodiimide) with the addition of about 1.1wt percent into a melt mixing kettle, and continuously stirring and mixing for about 10min to uniformly mix the molten glycolide and the reaction auxiliary agent to obtain a fluid premix; the premix in a fluid state is conveyed to a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (a sample is taken, and the weight average molecular weight of the glycolic acid prepolymer is about 5.03 ten thousand by GPC measurement), then the glycolic acid prepolymer is conveyed to tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and the material from the head of the tackifying equipment is subjected to liquid nitrogen quenching to obtain a polyglycolic acid product.

Preparation of example 6

Introducing molten crude glycolide into a falling-film evaporator (e.g., with a height of 40cm and a bottom diameter of 10 cm) at a feed rate of 500 g/hr, wherein the vacuum in the falling-film evaporator is set to an absolute pressure of about 5.0kPa, the heat exchange surface of the falling-film evaporator is a two-stage heat exchange surface, the temperatures of the heat exchange surfaces from top to bottom are respectively set to about 195 deg.C and about 198 deg.C, the average film-forming thickness of the material from top to bottom along the entire heat exchange surface is about 110 μm, the evaporation residence time of the material on the entire heat exchange surface is about 130s, transferring the glycolide material after evaporation purification into a centrifugal washer, washing, centrifuging, transferring the solid into a vacuum drier for vacuum drying (with an absolute pressure of 500Pa or less and 60 deg.C for 2 hr), pulverizing the dried solid by a pulverizer, and sieving by a sieve to obtain purified glycolide powder (D) ₉₀ Less than or equal to 200 mu m, the purity is more than or equal to 98 percent, and the acidity is less than or equal to 20 mmol/kg); then introducing the purified glycolide powder into a melting and mixing kettle, heating to about 116 ℃ under normal pressure, stirring and adding reaction auxiliary agents (based on the mass of the purified glycolide powder, the addition of the catalyst (stannous octoate) is about 4.2wt%, the addition of the initiator (formed by mixing isopropanol and benzyl alcohol according to a mass ratio of 4: 1) is about 5.0wt%, and the addition of the dehydrating agent (polycarbodiimide) is about 0.7 wt%) into the melting and mixing kettle in the existing injection mode within about 5min, and continuously stirring and mixing for about 10min to uniformly mix the molten glycolide and the reaction auxiliary agents to obtain a fluid premix; will be in the form of a flowThe premix in the form of body is conveyed into a static mixer through a melt metering pump for prepolymerization to obtain a glycolic acid prepolymer (the weight average molecular weight of the glycolic acid prepolymer is about 5.62 ten thousand by GPC measurement), then the glycolic acid prepolymer is conveyed into tackifying equipment (for example, a twin-screw extruder only provided with a devolatilization section) for final polymerization, and the material from the head of the tackifying equipment is quenched by liquid nitrogen to obtain the polyglycolic acid product.

The temperature parameters of the respective stages of the static mixer in examples 1-6 above are shown in the following tables 1-1:

TABLE 1-1

Item

Static mixer

First stage

Second section

Third stage

Fourth stage

Fifth stage

Preparation of example 1

Four sections in total

About 120 deg.C

About 190 deg.C

About 213 deg.C

About 224 deg.C

/

Preparation of example 2

Four sections in total

About 180 deg.C

About 209 deg.C

About 220 deg.C

About 230 deg.C

/

Preparation of example 3

Total five sections

About 150 deg.C

About 190 deg.C

About 202 deg.C

About 213 deg.C

About 220 deg.C

Preparation of example 4

Five sections in total

About 168 deg.C

About 200 deg.C

About 210 deg.C

About 220 deg.C

About 230 deg.C

Preparation of example 5

Three segments in total

About 190 deg.C

About 205 deg.C

About 221 deg.C

/

Preparation of example 6

Three segments in total

About 220 deg.C

About 238 deg.C

About 250 deg.C

/

The time required for the materials in the static mixer in the above preparation examples 1 to 6 to pass through the respective stages is shown in the following tables 1 to 2:

tables 1 to 2

The parameter settings of the devolatilization section in the tackifying apparatuses of preparation examples 1 to 6 described above are shown in Table 2 below:

TABLE 2

Item	Temperature (. Degree.C.)	Absolute pressure (Pa)	Length-diameter ratio of screw	Screw rotation speed (r/min)
					Preparation of example 1	About 235	100	52	30
Preparation of example 2	About 240	250	50	45
					Preparation of example 3	About 240	120	56	60
Preparation of example 4	About 236	150	60	30
					Preparation of example 5	About 221	380	50	45
Preparation of example 6	About 250 f	500	54	60

Note: the time for devolatilization of the glycolic acid prepolymer in the tackifying equipment in preparative examples 1-6 described above was about 15min.

The temperature settings of the respective lines from the melt mixing tank to the thickening apparatus in the above production examples 1 to 6 are shown in the following table 3:

TABLE 3

Note: the conveying flow rates of the melt metering pump and the melt pump used in the above-mentioned production examples 1 to 3 were each set to about 6.7L/h, and the conveying flow rates of the melt metering pump and the melt pump used in examples 4 to 6 were each set to about 5.3L/h.

Comparative example

The crude glycolide was purified using the following conventional recrystallization technique:

adding crude glycolide into a proper amount of acetone (the mass of the acetone is about 2-4 times of that of the crude glycolide), dissolving the glycolide at about 60 ℃, then filtering by using quantitative filter paper with the thickness of 1-3 mu m, reducing the temperature of the filtered liquid to about 20 ℃ at the rate of reducing the temperature by about 0.2 ℃ per minute, reducing the temperature to about-15 ℃ at the rate of reducing the temperature by about 0.4-0.5 ℃ per minute, wherein the total time of the temperature reduction process is about 5 hours, keeping the temperature for about 1 hour when the temperature is reduced to about-15 ℃, then carrying out suction filtration, solid-liquid separation, and repeating the steps for 2-4 times to obtain the purified glycolide (the purity is more than or equal to 98.5%, and the acidity is less than or equal to 20 mmol/kg).

Adding the purified glycolide obtained by the recrystallization technology into a double-screw extruder from a main feeding port, adding a reaction auxiliary agent through a side feeding port to ensure that the glycolide performs polymerization reaction in the double-screw extruder, and performing liquid nitrogen quenching on a material from a machine head of the double-screw extruder to obtain a polyglycolic acid product.

According to the above-described method, the temperatures of the respective stages in the twin-screw extruder employed in comparative examples 1 to 6 were set as shown in the following tables 4 to 1:

TABLE 4-1

Note: in comparative examples 1-6, the reaction aid was added in the first stage of the mixing section.

In the above comparative examples 1-6, the time for the material to pass through the first stage in the mixing stage was about 1min, the time to pass through the second stage was about 3min, and the time to pass through the third stage was about 6min, for a total of 10min; in the reaction section, the time for the material to pass through the first section is about 5min, the time for the material to pass through the second section is about 10min, the time for the material to pass through the third section is about 20min, and the time for the material to pass through the fourth section is about 45min, which is 80min in total; in the devolatilization section, the throughput time of the material was about 15min.

The screw length-diameter ratio, screw rotation speed and devolatilization pressure settings of the respective sections of the twin-screw extruders in the above comparative examples 1 to 6 are shown in the following tables 4 to 2:

TABLE 4-2

Item	Length to diameter ratio of mixing section screw	Length-diameter ratio of screw of reaction section	Length-diameter ratio of screw of devolatilization section	Screw rotation speed (r/min)	Absolute pressure of devolatilization section
						Comparative example 1	35	77	52	30	100Pa
Comparative example 2	32	75	50	45	250Pa
						Comparative example 3	40	80	56	60	120Pa
Comparative example 4	35	72	60	30	150Pa
						Comparative example 5	30	70	50	45	380Pa
Comparative example 6	32	77	54	60	500Pa

The reaction assistant used in comparative example 1 was the same as that used in example 1, and so on, and the reaction assistants used in comparative examples 2 to 6 were the same as those used in examples 2 to 6, respectively.

The molecular weights and distribution indexes of the polyglycolic acid obtained in the above preparation examples 1 to 6 and comparative examples 1 to 6 are measured as shown in the following table 5:

TABLE 5

Item	Preparation of example 1	Preparation of example 2	Preparation of example 3	Preparation of example 4	Preparation of example 5	Preparation of example 6
							Number average molecular weight (Mn)	144754	152544	155367	133346	105497	108446
Weight average molecular weight (Mw)	178048	190680	186440	162682	135036	142065
							Molecular weight distribution index	1.23	1.25	1.20	1.22	1.28	1.31
Item	Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6
							Number average molecular weight (Mn)	98559	96094	96884	100055	72145	82748
Weight average molecular weight (Mw)	166565	160477	157922	160088	132026	140672
							Molecular weight distribution index	1.69	1.67	1.63	1.60	1.83	1.70

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the scope of the invention, which is defined by the claims appended hereto, and any other technical entity or method that is encompassed by the claims as broadly defined herein, or equivalent variations thereof, is contemplated as being encompassed by the claims.

Claims

1. An apparatus for preparing narrow molecular weight distribution polyglycolic acid comprises a melt mixing kettle, a static mixer connected with a discharge port of the melt mixing kettle, and a tackifying device arranged at the downstream of the static mixer.

2. The apparatus of claim 1, wherein the apparatus has a reaction additive storage tank connected to the melt mixing kettle feed port; and a melt metering pump is arranged between the discharge port of the melting mixing kettle and the static mixer.

3. The apparatus of claim 1, wherein the static mixer is coupled to the viscosity building device via a material transport assembly; the material conveying assembly comprises a material conveying pipeline, a melt pump and a cleaning liquid dredging pipe, wherein the material conveying pipeline is used for connecting the discharge hole of the static mixer with the feed hole of the tackifying device, the melt pump is arranged on the material conveying pipeline, and the cleaning liquid dredging pipe is connected with the melt pump in parallel on the material conveying pipeline.

4. The apparatus of any one of claims 1-3, further comprising a falling film evaporation purification unit disposed upstream of and coupled to the melt-mixing kettle.

5. The apparatus of claim 4, wherein the falling film evaporation purification unit comprises a falling film evaporator and a screen, wherein the outlet at the bottom of the screen is connected to the inlet at the top of the melt mixing kettle.

6. A method for the preparation of narrow molecular weight distribution polyglycolic acid by the device of any one of claims 1 to 5, comprising the steps of:

(2) Prepolymerizing the fluid premix obtained in step (1) in a static mixer to obtain a glycolic acid prepolymer;

(3) And (3) finally polymerizing the glycolic acid prepolymer obtained in the step (2) through a tackifying device to obtain polyglycolic acid.

7. The method according to claim 6, wherein the glycolide used in the step (1) has a purity of 98% or more and an acidity of 20mmol/kg or less.

8. The method of claim 6, wherein the static mixer used in step (2) employs at least 2 stages of gradient temperature ramp.

9. The method of claim 8, wherein the first stage temperature ranges from 120 ℃ to 220 ℃; the temperature of the last stage is 220-250 ℃.

10. The method of claim 6, wherein the tackifying apparatus in step (3) is devolatilized at an absolute pressure of less than or equal to 500Pa and a temperature of from 220 ℃ to 250 ℃.

11. The process according to any one of claims 6 to 10, wherein the glycolide of step (1) is obtained by subjecting the molten crude glycolide to evaporation purification by means of a falling-film evaporator.

12. The method of claim 11, wherein the falling film evaporator contains n heat exchange devices, n being an integer greater than or equal to 2; the temperature of the n heat exchange devices increases along the flow direction of the molten crude glycolide in a gradient manner.

13. The method of claim 12, wherein the heat exchange device has an average film thickness of no more than 300 μ ι η.