CN115386032A - Preparation method and reaction device of polyethylene-vinyl alcohol resin - Google Patents
Preparation method and reaction device of polyethylene-vinyl alcohol resin Download PDFInfo
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- 239000004698 Polyethylene Substances 0.000 claims 1
- -1 polyethylene Polymers 0.000 claims 1
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- 239000000178 monomer Substances 0.000 abstract description 34
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- OZAIFHULBGXAKX-UHFFFAOYSA-N 2-(2-cyanopropan-2-yldiazenyl)-2-methylpropanenitrile Chemical compound N#CC(C)(C)N=NC(C)(C)C#N OZAIFHULBGXAKX-UHFFFAOYSA-N 0.000 description 13
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F218/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid
- C08F218/02—Esters of monocarboxylic acids
- C08F218/04—Vinyl esters
- C08F218/08—Vinyl acetate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01F—MIXING, e.g. DISSOLVING, EMULSIFYING OR DISPERSING
- B01F33/00—Other mixers; Mixing plants; Combinations of mixers
- B01F33/70—Mixers specially adapted for working at sub- or super-atmospheric pressure, e.g. combined with de-foaming
- B01F33/71—Mixers specially adapted for working at sub- or super-atmospheric pressure, e.g. combined with de-foaming working at super-atmospheric pressure, e.g. in pressurised vessels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
- B01J3/002—Component parts of these vessels not mentioned in B01J3/004, B01J3/006, B01J3/02 - B01J3/08; Measures taken in conjunction with the process to be carried out, e.g. safety measures
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
- B01J3/04—Pressure vessels, e.g. autoclaves
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F2/00—Processes of polymerisation
- C08F2/01—Processes of polymerisation characterised by special features of the polymerisation apparatus used
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F210/00—Copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
- C08F210/02—Ethene
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F8/00—Chemical modification by after-treatment
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- Health & Medical Sciences (AREA)
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- Polymers & Plastics (AREA)
- General Chemical & Material Sciences (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
Abstract
The invention provides a preparation method and a reaction device of polyethylene-vinyl alcohol resin, belongs to the technical field of preparation processes of high-molecular copolymers, and can solve the technical problems of low production efficiency, unstable reaction and low monomer conversion rate of the traditional polymerization method of EVOH resin. The technical scheme comprises the following steps: injecting vinyl acetate, an initiator and a reaction solvent into a high-pressure mixer, and fully mixing to obtain a mixture; injecting the mixture into a first reaction kettle, and adjusting the pressure and temperature of the first reaction kettle to obtain a first-stage reaction polymerization solution; injecting the first-stage reaction polymerization liquid into a second reaction kettle, adjusting the pressure and the temperature of the second reaction kettle, and intermittently adding an initiator and a reaction solvent to obtain a second-stage reaction polymerization liquid; stopping the reaction, cooling, collecting the polymerization solution, and performing reduced pressure distillation, saponification, precipitation and cleaning to obtain the polyethylene-vinyl alcohol resin finished product. The invention can be applied to the preparation of polyethylene-vinyl alcohol resin.
Description
Technical Field
The invention belongs to the technical field of preparation processes of high-molecular copolymers, and particularly relates to a preparation method and a reaction device of polyethylene-vinyl alcohol resin.
Background
Polyethylene-vinyl alcohol resin (abbreviated as "EVOH resin", also known as Ethylene vinyl alcohol polymer, english name Ethylene vinyl alcohol copolymer). EVOH resin is a high-barrier material with wide application and excellent performance, and is mainly applied to packaging of foods, medicines, cosmetics, oil tanks and the like. EVOH resin has the remarkable characteristics of excellent barrier property and good processability to gas, and products thereof have excellent transparency, glossiness, wear resistance and cold resistance. The barrier and processing properties of EVOH depend primarily on the proportion of ethylene in the polymer, with an increase in the proportion of ethylene enhancing processing properties and also reducing gas barrier properties. Because the barrier property and the processability of EVOH mainly depend on the proportion of ethylene in the polymer, the properties of the polymers with different ethylene contents have large difference, and the problems of yellowing or crystal points and the like also occur in the later processing process. Controlling the ethylene content and molecular weight distribution in polymers in continuous polymerization processes has been a major and difficult point that has plagued their production.
Although the synthesis technology of EVOH copolymer has been greatly advanced after decades of development, the main technology still faces the technical blockade of related national enterprises. At present, only the product of the Japan Coly company has the best stability and processability and the highest market share, other manufacturers have certain gaps in quality and performance although producing corresponding products, and domestic enterprises have developed EVOH research for many years but have not realized industrialization so far. The preparation of EVOH resin mainly comprises polymerization and re-saponification processes, but the polymerization reaction process has the problems of low production efficiency, unstable reaction, high energy consumption in later monomer and solvent recovery treatment, high total production process cost and the like.
Therefore, it is a key to solve the above problems to develop a method for preparing a polyethylene-vinyl alcohol resin, which has high production efficiency, more stable polymer production, higher monomer conversion rate, reduced solvent recovery throughput, and controllable cost.
Disclosure of Invention
The invention provides a preparation method and a reaction device of polyethylene-vinyl alcohol resin aiming at the technical problems of low production efficiency, unstable reaction and low monomer conversion rate of the traditional polymerization method of EVOH resin, wherein the method adopts two reaction kettle polymerization reaction devices which are connected in series in a grading way, and provides larger buffer space for polymerization reaction by controlling polymerization conditions in different reaction kettles, so that the polymer production is more stable, the monomer conversion rate is higher, the solvent recovery processing amount is reduced, and the production cost is effectively reduced. The invention has great promotion effect on the research and development and production of domestic polyethylene-vinyl alcohol resin.
In order to achieve the purpose, the invention adopts the technical scheme that:
the preparation method of the polyethylene-vinyl alcohol resin is carried out by adopting two reaction kettle polymerization reaction devices which are connected in series in a grading way, and comprises the following steps:
injecting ethylene gas into the high-pressure mixer, the first reaction kettle and the second reaction kettle;
injecting vinyl acetate, an initiator and a reaction solvent into the high-pressure mixer, and fully mixing to obtain a mixture;
injecting the mixture into a first reaction kettle, adjusting the pressure and the temperature of the first reaction kettle, and controlling the conversion rate of vinyl acetate monomer to be 10-50% to obtain a first-stage reaction polymerization liquid;
injecting the first-stage reaction polymerization liquid into a second reaction kettle, adjusting the pressure and the temperature of the second reaction kettle, intermittently adding an initiator and a reaction solvent, and controlling the conversion rate of a vinyl acetate monomer to be 30-90% to obtain a second-stage reaction polymerization liquid;
adding a polymerization inhibitor into the second-stage reaction polymerization liquid to terminate the reaction, and cooling and collecting the polymerization liquid;
and (3) carrying out reduced pressure distillation, saponification reaction and precipitation and cleaning treatment on the polymerization solution in sequence to obtain the finished product of the polyethylene-vinyl alcohol resin.
In an embodiment, the first reaction kettle and the second reaction kettle are both fully mixed flow reaction kettles, and the first reaction kettle and the second reaction kettle are both provided with a pressure reducing valve.
In one embodiment, the feeding modes of the first reaction kettle and the second reaction kettle are both continuous feeding, and the pressure of the high-pressure mixer is 2-8Mpa.
In one embodiment, the pressure of the first reaction kettle is 2-8MPa, the temperature is 50-90 ℃, and the retention time is 0.5-5h; the pressure of the second reaction kettle is 1-7MPa, the temperature is 40-100 ℃, and the retention time is 1-5h.
In one embodiment, the pressure of the first reaction kettle is 3-7MPa, the temperature is 50-80 ℃, and the retention time is 0.5-3h; the pressure of the second reaction kettle is 2-6MPa, the temperature is 50-80 ℃, and the retention time is 1-3h.
In one embodiment, the initiator is selected from azo initiators or peroxide initiators, and the reaction solvent is methanol or a mixture of methanol and an alcoholic solvent with 2-4 carbon atoms, wherein the mixture contains 50-98% of methanol and 2-50% of alcoholic solvent with 2-4 carbon atoms.
In one embodiment, before the reaction starts, the first reaction kettle and the second reaction kettle are cleaned by methanol for 1-3 times, then the first reaction kettle and the second reaction kettle are replaced by nitrogen for 5-15min, then the first reaction kettle and the second reaction kettle are vacuumized to the pressure of-0.08 to-0.1 MPa of the first reaction kettle and the second reaction kettle, and finally ethylene gas is used for replacing for 1-2 times.
In one embodiment, the termination reaction is: inputting the second-stage reaction polymerization liquid into a buffer tank, starting a high-pressure pump to inject a polymerization inhibitor solution into the second-stage reaction polymerization liquid, metering the mass of liquid inlet, stopping the reaction, slowly adjusting a pressure reducing valve until gas is discharged when the temperature of the buffer tank is reduced to below 25 ℃, adjusting the pressure reducing valve in a gradient manner until the pressure of the buffer tank is 0Mpa, and collecting the polymerization liquid.
In one embodiment, the reduced pressure distillation is: continuously adding methanol or methanol steam into the polymerization solution to remove unreacted vinyl acetate monomer, and ensuring that the content of vinyl acetate in the polymer is lower than 100ppm;
the saponification reaction comprises the following steps: adding 1-20% alkaline methanol solution into 5-35% solid content polymerization solution, continuously adding methanol or methanol vapor, timely discharging generated methyl acetate, and adding a certain amount of acetic acid into a reaction system after the reaction is finished to adjust the pH value of the solution to 5 to obtain alcoholic solution;
the precipitation cleaning treatment comprises the following steps: and (3) precipitating the alcoholysis solution in 4-12 times of cold water, washing for 2-3 times by using the same amount of water precipitated, and drying the washed polymer in a vacuum oven at 60-100 ℃ for 2-8h to obtain the polyethylene-vinyl alcohol resin finished product.
The present invention also provides a polymerization reaction apparatus for preparing the polyethylene-vinyl alcohol resin according to any one of the above embodiments, comprising:
a high-pressure mixer used for uniformly mixing the vinyl acetate, the initiator and the reaction solvent,
a feed inlet of the first reaction kettle is connected with a discharge outlet of the high-pressure mixer and is used for preparing a first-section reaction polymerization liquid,
a second reaction vessel having a feed inlet connected to the discharge outlet of the first reaction vessel for preparing a second-stage reaction polymerization solution, and
a feed inlet of the buffer tank is connected with a discharge outlet at the bottom of the second reaction kettle and is used for carrying out termination reaction on the second-stage reaction polymerization liquid;
the pressure reducing valves are installed on the first reaction kettle and the second reaction kettle, and a high-pressure pump is arranged on a pipeline between a discharge port of the first reaction kettle and the second reaction kettle.
Compared with the prior art, the invention has the advantages and positive effects that:
1. the preparation method of the polyethylene-vinyl alcohol resin and the reaction device provided by the invention are carried out by adopting two reaction kettle polymerization reaction devices which are connected in series in a grading way, and a larger buffer space is provided for the polymerization reaction by controlling the polymerization conditions in different reaction kettles, so that the polymer production is more stable, the monomer conversion rate is higher, the solvent recovery treatment amount is reduced, and the production cost is effectively reduced;
2. the preparation method of the polyethylene-vinyl alcohol resin provided by the invention can effectively control the reaction rate, avoids the problems of difficult control of the polymerization rate, wide molecular weight distribution and the like caused by high conversion rate in the later polymerization stage of a single reaction kettle, enables the polymer production to be more stable, the monomer conversion rate to be higher, reduces the solvent recovery processing amount, effectively reduces the production cost, improves the production efficiency, and reduces the residues of the monomer and the initiator, thereby reducing the production cost.
Drawings
FIG. 1 is a schematic structural diagram of a polymerization apparatus for preparing a polyethylene-vinyl alcohol resin according to an embodiment of the present invention.
In the upper drawing:
1. a high-pressure mixer; 2. a first reaction kettle; 3. a second reaction kettle; 4. a pressure reducing valve; 5. a high pressure pump; 6. and (6) caching the slots.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a preparation method of polyethylene-vinyl alcohol resin, which is carried out by adopting two reaction kettle polymerization reaction devices connected in series in a grading way, and comprises the following steps:
s1, injecting ethylene gas into a high-pressure mixer, a first reaction kettle and a second reaction kettle;
before formally injecting ethylene gas into each reaction device in the step S1, the method also comprises a pretreatment process, namely before the reaction starts, the first reaction kettle and the second reaction kettle are cleaned by methanol for 1-3 times, then nitrogen is used for purging for 5-15min, the first reaction kettle and the second reaction kettle are replaced, the first reaction kettle and the second reaction kettle are vacuumized to the pressure of-0.1 Mpa of the first reaction kettle and the second reaction kettle, and finally the ethylene gas is used for replacing for 1-2 times.
S2, injecting vinyl acetate, an initiator and a reaction solvent into the high-pressure mixer, and fully mixing to obtain a mixture;
in the step S2, the initiator is selected from azo initiators or peroxide initiators, preferably azo initiators, and the reaction solvent is methanol or a mixture of methanol and an alcohol solvent with 2-4 carbon atoms, wherein the methanol accounts for 50-98% of the mixture, and the alcohol solvent with 2-4 carbon atoms accounts for 2-50%.
S3, injecting the mixture into a first reaction kettle, adjusting the pressure and the temperature of the first reaction kettle, and controlling the conversion rate of vinyl acetate monomers to be 10-50% to obtain a first-stage reaction polymerization solution;
in the step S3, the conversion rate of vinyl acetate monomer in the first-stage reaction is controlled to be 10-50% by controlling the parameters such as temperature and pressure of the first reaction vessel, and the obtained first-stage reaction polymerization liquid directly enters the second reaction vessel for subsequent reaction.
S4, injecting the first-stage reaction polymerization liquid into a second reaction kettle, adjusting the pressure and the temperature of the second reaction kettle, intermittently adding an initiator and a reaction solvent, and controlling the conversion rate of a vinyl acetate monomer to be 30-90% to obtain a second-stage reaction polymerization liquid;
in the step S4, by controlling the temperature, pressure and other technical parameters of the second reaction kettle, the monomer conversion rate of vinyl acetate in the second-stage reaction is controlled to be 30-90%, which can significantly improve the production efficiency and monomer conversion rate, the monomer conversion rate can reach more than 80%, and the cost of later-stage monomer removal and recovery treatment is effectively reduced.
S5, adding a polymerization inhibitor into the second-stage reaction polymerization liquid to terminate the reaction, and cooling and collecting the polymerization liquid;
in the step S5, the termination reaction is: inputting the second-stage reaction polymerization liquid into a buffer tank, starting a high-pressure pump to inject a polymerization inhibitor solution into the second-stage reaction polymerization liquid, metering the mass of liquid inlet, stopping the reaction, slowly adjusting a pressure reducing valve until gas is discharged when the temperature of the buffer tank is reduced to below 25 ℃, adjusting the pressure reducing valve in a gradient manner until the pressure of the buffer tank is 0Mpa, and collecting the polymerization liquid. In addition, considering that the polymerization inhibitor used in the termination reaction of the present invention is a chemical reagent commonly used in the chemical field, the present invention does not specifically limit the specific type of the polymerization inhibitor, and a person skilled in the art can select the polymerization inhibitor according to the reagent requirements. In addition, it should be noted here that, in the present invention, the first reaction kettle and the second reaction kettle are a continuous reaction system, the polymerization inhibitor is added in the step S5, instead of being added in the second reaction kettle, the polymerization solution in the second stage reaction is input into another special buffer tank for reaction, the reaction is terminated after the polymerization inhibitor is added, and the polymerization solution is collected after being cooled.
And S6, sequentially carrying out reduced pressure distillation, saponification reaction and precipitation cleaning on the polymerization solution to prepare the polyethylene-vinyl alcohol resin finished product.
In the step S6, the reduced pressure distillation is: continuously adding methanol or methanol steam into the polymerization solution to remove unreacted vinyl acetate monomer, and ensuring that the content of vinyl acetate in the polymer is lower than 100ppm;
the saponification reaction comprises the following steps: adding 1-20% alkaline methanol solution into 5-35% solid content polymer solution, continuously adding methanol or methanol vapor, timely discharging generated methyl acetate, and adding a certain amount of acetic acid into a reaction system after the reaction is finished to adjust the pH of the solution to 5 to obtain an alcoholysis solution;
the precipitation cleaning treatment comprises the following steps: and (3) precipitating the alcoholysis solution in 4-12 times of cold water, washing for 2-3 times by using the same amount of water precipitated, and drying the washed polymer in a vacuum oven at 60-100 ℃ for 2-8h to obtain the polyethylene-vinyl alcohol resin finished product.
In a specific embodiment, the first reaction kettle and the second reaction kettle are both fully mixed flow reaction kettles, and the first reaction kettle and the second reaction kettle are both provided with pressure reducing valves.
In a specific embodiment, the feeding modes of the first reaction kettle and the second reaction kettle are both continuous feeding, and the pressure of the high-pressure mixer is 2-8Mpa.
In the above embodiment, it is within the scope of the present invention to select the pressure of the high-pressure mixer to be 2Mpa, 3Mpa, 4Mpa, 5Mpa, 6Mpa, 7Mpa, 8Mpa or any value within the above-defined range according to actual requirements.
In a specific embodiment, the pressure of the first reaction vessel is 2 to 8MPa, preferably 3 to 7MPa, the temperature is 50 to 90 ℃, preferably 50 to 80 ℃, and the residence time is 0.5 to 5 hours, preferably 0.5 to 3 hours; the pressure of the second reaction kettle is 1-7MPa, preferably 2-6MPa, the temperature is 40-100 ℃, preferably 50-80 ℃, and the retention time is 1-5h, preferably 1-3h.
In the above embodiment, the pressure of the first reaction vessel may be selected to be 2Mpa, 3Mpa, 4Mpa, 5Mpa, 6Mpa, 7Mpa, 8Mpa or any value selected from the above-mentioned limited ranges according to actual requirements, the temperature may be selected to be 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃ or any value selected from the above-mentioned limited ranges according to actual requirements, and the residence time may be selected to be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h or any value selected from the above-mentioned limited ranges according to actual requirements; the pressure of the second reaction kettle can be selected from 1Mpa, 2Mpa, 3Mpa, 4Mpa, 5Mpa, 6Mpa and 7Mpa or any value within the above limited range according to actual needs, the temperature can be selected from 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, 100 ℃ or any value within the above limited range according to actual needs falls within the protection range of the invention, and the retention time can be selected from 1h, 2h, 3h, 4h and 5h or any value within the above limited range according to actual needs falls within the protection range of the invention.
The present invention also provides a polymerization reaction apparatus for preparing the polyethylene-vinyl alcohol resin according to any one of the above embodiments, comprising:
a high-pressure mixer 1 for uniformly mixing vinyl acetate, an initiator and a reaction solvent,
a first reaction kettle 2, the feed inlet of which is connected with the discharge outlet of the high-pressure mixer 1 and is used for preparing a first-stage reaction polymerization liquid,
a second reaction vessel 3, the feed inlet of which is connected with the discharge outlet of the first reaction vessel 2, for preparing a second-stage reaction polymerization liquid, and
a feed inlet of the buffer tank 6 is connected with a discharge outlet at the bottom of the second reaction kettle 3 and is used for terminating the second-stage reaction polymerization liquid;
the pressure reducing valve 4 is installed on the first reaction kettle 2 and the second reaction kettle 3, and the high-pressure pump 5 is arranged on a pipeline between the discharge port of the first reaction kettle 2 and the second reaction kettle 3.
In order to more clearly describe the preparation method of the polyethylene-vinyl alcohol resin provided in the examples of the present invention in detail, the following description will be given with reference to the specific examples.
Example 1
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 9min, replacing, vacuumizing to-0.1 Mpa, and replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle 2 to be 3.4MPa, setting automatic control, starting a high-pressure pump 5 to inject 0.2 part of azodiisobutyronitrile, 110 parts of methanol, 10 parts of ethanol and 400 parts of vinyl acetate into the high-pressure mixer 1 for full dissolution, then entering the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 72 ℃, the reaction retention time to be 1.5h, and the conversion rate of vinyl acetate monomer to be 35%, so as to obtain a section of reaction polymerization liquid;
pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 3.1MPa, adjusting the temperature of the reaction kettle to be 65 ℃, and intermittently adding 0.05 part of azobisisobutyronitrile and 20 parts of methanol solution for 3.5 hours with the conversion rate of vinyl acetate monomer of 75 percent to obtain a second-stage reaction polymerization liquid;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, then injecting 0.5 part of hydroquinone polymerization inhibitor solution into the second-stage reaction polymerization liquid, stopping the reaction, slowly adjusting a pressure reducing valve until ethylene gas is discharged when the temperature of the polymerization liquid is reduced to below 25 ℃, and collecting the polymerization liquid when the pressure of the buffer tank 6 is 0Mpa by adjusting the pressure reducing valve in a gradient manner;
(4) Removing vinyl acetate monomers: continuously adding methanol steam in a reduced pressure distillation mode to remove unreacted vinyl acetate monomers, and ensuring that the content of the vinyl acetate monomers in the polymer is lower than 100ppm;
(5) And (3) saponification reaction: adding 8% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; after the reaction is finished, adding a certain amount of acetic acid into the reaction system for neutralization until the pH is approximately equal to 5;
(6) Precipitation and cleaning: after the alcohol hydrolyzed solution is separated out in 8 times of water, the alcohol hydrolyzed solution is washed for 3 times by using the same amount of water separated out; and (3) drying the washed polymer in a vacuum oven at 85 ℃ for 6h to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Example 2
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 10min, replacing, vacuumizing to-0.09 Mpa, and replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle 2 to be 5.5MPa, setting automatic control, starting a high-pressure pump 5 to inject a mixed solution of 0.3 part of azodiisobutyronitrile, 120 parts of methanol, 40 parts of tert-butyl alcohol and 450 parts of vinyl acetate into the high-pressure mixer 1 for full dissolution, then feeding the mixed solution into the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 68 ℃, the reaction residence time to be 3.5 hours, and the conversion rate of vinyl acetate monomer to be 30%, so as to obtain a section of reaction polymerization liquid;
pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 5.0MPa, adjusting the temperature of the reaction kettle to be 66 ℃, and intermittently adding 0.05 part of azobisisobutyronitrile and 30 parts of methanol solution, wherein the reaction retention time is 4.0h, the conversion rate of vinyl acetate monomer is 80%, and obtaining a second-stage reaction polymerization liquid;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, starting a high-pressure pump 5 to inject 0.6 part of hydroquinone polymerization inhibitor solution into the second-stage reaction polymerization liquid, and stopping the reaction; when the temperature of the polymerization liquid is reduced to below 25 ℃, slowly adjusting a pressure reducing valve until ethylene gas is discharged, and adjusting the pressure reducing valve to the pressure of the buffer tank 6 to be 0Mpa in a gradient manner, and collecting the polymerization liquid;
(4) Removing vinyl acetate monomers: continuously adding methanol or methanol steam in a reduced pressure distillation mode to remove unreacted vinyl acetate monomers, and ensuring that the content of the vinyl acetate monomers in the polymer is lower than 100ppm;
(5) Saponification reaction: adding 8% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; at the end of the reaction, a certain amount of acetic acid was added to the reaction system to neutralize to pH 5.
(6) Separating out and cleaning: after the alcoholic hydrolysate is separated out in 10 times of water, washing for 2 times by using the same amount of deionized water; and (3) drying the washed polymer in a vacuum oven at 85 ℃ for 6h to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Example 3
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 10min, replacing, vacuumizing to-0.1 Mpa, and replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle to be 5.0MPa, starting a high-pressure pump 5 to inject 0.2 part of azobisisoheptonitrile, 90 parts of methanol, 30 parts of tert-butyl alcohol and 350 parts of vinyl acetate into the high-pressure mixer 1 to be fully dissolved, then entering the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 56 ℃, closing an ethylene inlet valve after the pressure is stabilized, controlling the reaction time to be 2.0h, and controlling the conversion rate of a vinyl acetate monomer to be 45% to obtain a section of reaction polymerization liquid;
pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 4.6MPa, adjusting the temperature of the reaction kettle to be 53 ℃, closing an ethylene inlet valve after the pressure is stable, adding 0.05 part of azodiisoheptonitrile and 40 parts of methanol solution, reacting for 3.5 hours, and obtaining a second-stage reaction polymerization liquid, wherein the conversion rate of vinyl acetate monomers is 85%;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, starting a high-pressure pump 5 to inject 0.6 part of hydroquinone polymerization inhibitor solution into the second-stage reaction polymerization liquid, and stopping the reaction; when the temperature of the polymerization liquid is reduced to below 25 ℃, slowly adjusting a pressure reducing valve until ethylene gas is discharged, and adjusting the pressure reducing valve to a pressure of 0Mpa in a buffer tank 6 in a gradient manner, and collecting the polymerization liquid;
(4) Removing vinyl acetate monomers: continuously adding methanol or methanol steam in a reduced pressure distillation mode to remove unreacted vinyl acetate monomers, and ensuring that the content of the vinyl acetate monomers in the polymer is lower than 100ppm;
(5) And (3) saponification reaction: adding 10% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; after the reaction is finished, adding a certain amount of acetic acid into the reaction system for neutralization until the pH is approximately equal to 5;
(6) Precipitation and cleaning: after the alcoholic hydrolysate is separated out in 8 times of water, washing for 2 times by using the same amount of deionized water; and (3) drying the washed polymer in a vacuum oven at 85 ℃ for 6 hours to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Example 4
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 10min, replacing the reaction kettle, vacuumizing to-0.1 MPa, and finally replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle 2 to be 3.8MPa, starting a high-pressure pump 5 to inject 0.25 part of azodiisobutyronitrile, 100 parts of methanol, 10 parts of ethanol and 350 parts of vinyl acetate into the high-pressure mixer 1 for full dissolution, then entering the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 63 ℃, closing an ethylene inlet valve after the pressure is stable, keeping the reaction for 3.5 hours, and obtaining 42% of vinyl acetate monomer conversion rate to obtain a section of reaction polymerization liquid;
pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 4.6MPa, adjusting the temperature of the reaction kettle to be 67 ℃, closing an ethylene inlet valve after the pressure is stable, adding 0.05 part of azodiisobutyronitrile and 30 parts of methanol solution, keeping the time for 4.5 hours, and obtaining a second-stage reaction polymerization liquid, wherein the conversion rate of vinyl acetate monomers is 87%;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, starting a high-pressure pump 5 to inject 0.8 part of hydroquinone polymerization inhibitor solution into the second-stage reaction polymerization liquid, and stopping the reaction; when the temperature of the reaction kettle is reduced to below 25 ℃, slowly adjusting a pressure reducing valve until ethylene gas is discharged, and adjusting the pressure reducing valve to the pressure of the buffer tank 6 to be 0Mpa in a gradient manner, and collecting polymerization liquid;
(4) Removing vinyl acetate monomers: continuously adding methanol or methanol steam in a reduced pressure distillation mode to remove unreacted vinyl acetate monomers, and ensuring that the content of the vinyl acetate monomers in the polymer is lower than 100ppm;
(5) And (3) saponification reaction: adding 10% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; adding a certain amount of acetic acid into the reaction system to neutralize until the pH is =5 after the reaction is finished;
(6) Precipitation and cleaning: after the alcoholic hydrolysate is separated out in 8 times of water, washing for 2 times by using the same amount of deionized water; and (3) drying the washed polymer in a vacuum oven at 90 ℃ for 7h to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Example 5
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 9min, replacing the reaction kettle, vacuumizing to-0.1 MPa, and finally replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle 2 to be 3.2MPa, setting automatic control, starting a high-pressure pump 5 to continuously inject reaction solution (0.2 part of azodiisobutyronitrile, 120 parts of methanol and 400 parts of vinyl acetate mixed solution) into the high-pressure mixer, fully dissolving the reaction solution, then introducing the reaction solution into the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 58 ℃, the reaction retention time to be 3 hours, and the conversion rate of vinyl acetate monomer to be 35% to obtain a section of reaction polymerization liquid;
continuously pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 3.0MPa, adjusting the temperature of the reaction kettle to be 65 ℃, continuously adding 0.05 part of azobisisobutyronitrile and 20 parts of methanol solution, keeping the time for 3.5 hours, and obtaining a second-stage reaction polymerization liquid, wherein the conversion rate of vinyl acetate monomers is 75%;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, starting a high-pressure pump 5, injecting 0.5 part of hydroquinone polymerization inhibitor into the second-stage reaction polymerization liquid, and stopping the reaction; when the temperature of the polymerization liquid is reduced to below 25 ℃, slowly adjusting a pressure reducing valve until ethylene gas is discharged, and adjusting the pressure reducing valve to a pressure of 0Mpa in a buffer tank 6 in a gradient manner, and collecting the polymerization liquid;
(4) Removing vinyl acetate monomers: continuously adding methanol vapor to remove unreacted vinyl acetate monomer by using a reduced pressure distillation mode, and ensuring that the content of the vinyl acetate monomer in the polymer is lower than 100ppm;
(5) And (3) saponification reaction: adding 8% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; after the reaction is finished, adding a certain amount of acetic acid into the reaction system for neutralization until the pH is approximately equal to 5;
(6) Separating out and cleaning: after the alcohol hydrolyzed solution is separated out in 6 times of water, the alcohol hydrolyzed solution is washed for 2 times by using the same amount of water separated out; and (3) drying the washed polymer in a vacuum oven at 75 ℃ for 10h to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Example 6
The embodiment provides a preparation method of polyethylene-vinyl alcohol resin, which specifically comprises the following steps:
(1) Cleaning a reaction kettle and deoxidizing and replacing: cleaning the reaction kettle with methanol for 3 times, purging with nitrogen for 9min, replacing the reaction kettle, vacuumizing to-0.1 MPa, and finally replacing with ethylene gas for 2 times;
(2) Feeding and reacting: starting a pneumatic booster pump to inject ethylene gas into a high-pressure mixer 1, a first reaction kettle 2 and a second reaction kettle 3, controlling the pressure of the first reaction kettle 2 to be 5.0MPa, setting automatic control, starting a high-pressure pump 5 to continuously inject reaction solution (0.35 parts of azodiisobutyronitrile, 120 parts of methanol, 10 parts of tert-butyl alcohol and 300 parts of vinyl acetate mixed solution) into the high-pressure mixer 1, fully dissolving, then injecting the reaction solution into the first reaction kettle 2, adjusting the temperature of the reaction kettle to be 67 ℃, keeping the reaction time to be 3.0h, and converting the vinyl acetate monomer to 50% to obtain a section of reaction polymerization liquid;
continuously pumping the first-stage reaction polymerization liquid into a second reaction kettle 3 through a high-pressure pump 5, controlling the pressure of the second reaction kettle 3 to be 5.6MPa, adjusting the temperature of the reaction kettle to be 72 ℃, and continuously adding 0.07 part of azodiisobutyronitrile and 30 parts of methanol solution, wherein the retention time is 1.5h, the conversion rate of vinyl acetate monomers is 83%, so as to obtain a second-stage reaction polymerization liquid;
(3) And (3) finishing the reaction: inputting the second-stage reaction polymerization liquid obtained in the step (2) into a buffer tank 6, starting a high-pressure pump 5, injecting 0.5 part of hydroquinone polymerization inhibitor into the second-stage reaction polymerization liquid, and stopping the reaction; when the temperature of the polymerization liquid is reduced to below 25 ℃, slowly adjusting a pressure reducing valve until ethylene gas is discharged, and adjusting the pressure reducing valve to the pressure of the buffer tank 6 to be 0Mpa in a gradient manner, and collecting the polymerization liquid;
(4) Removing vinyl acetate monomers: continuously adding methanol steam in a reduced pressure distillation mode to remove unreacted vinyl acetate monomers, and ensuring that the content of the vinyl acetate monomers in the polymer is lower than 100ppm;
(5) And (3) saponification reaction: adding 8% sodium hydroxide (relative to the molar weight of vinyl acetate) methanol solution into the polymerization solution with the solid content of 30%, continuously adding methanol, and timely discharging the generated methyl acetate; after the reaction is finished, adding a certain amount of acetic acid into the reaction system for neutralization until the pH is approximately equal to 5;
(6) Separating out and cleaning: after the alcoholic hydrolysate is separated out in 10 times of water, washing for 2 times by using the same amount of water separated out; and (3) drying the washed polymer in a vacuum oven at 85 ℃ for 7 hours to obtain an EVOH resin finished product, wherein the product parameters are shown in Table 1.
Performance test
The invention also carries out various performance tests on the EVOH resin finished product prepared in each embodiment, and the specific test method and test results are as follows:
the test method comprises the following steps: the ethylene content is measured by adopting an H-NMR method and then calculated, the molecular weight is measured by adopting a liquid gel chromatograph, the chromaticity is directly measured by adopting a light splitting color meter, and the melt index is measured by adopting a melt flow rate meter;
and (3) testing results: see table 1.
TABLE 1 production parameters of EVOH resin products obtained in examples 1-6
As can be seen from the analysis of the data in Table 1, the invention adopts two reaction kettle polymerization reaction devices which are connected in series in a grading way, and provides larger buffer space for polymerization reaction by controlling the polymerization conditions in different reaction kettles, so that the polymer production is more stable, the monomer conversion rate is higher, the solvent recovery processing amount is reduced, and the production cost is effectively reduced. The invention has great promotion effect on the research and development and production of domestic polyethylene-vinyl alcohol resin. The invention can obtain EVOH samples with different compositions and molecular weights by controlling different polymerization conditions, and has uniform molecular weight distribution, low resin chroma and excellent processability.
Claims (10)
1. The preparation method of the polyethylene-vinyl alcohol resin is characterized by adopting two reaction kettle polymerization reaction devices which are connected in series in a grading way, and comprises the following steps:
injecting ethylene gas into the high-pressure mixer, the first reaction kettle and the second reaction kettle;
injecting vinyl acetate, an initiator and a reaction solvent into the high-pressure mixer, and fully mixing to obtain a mixture;
injecting the mixture into a first reaction kettle, adjusting the pressure and the temperature of the first reaction kettle, and controlling the conversion rate of vinyl acetate monomer to be 10-50% to obtain a first-stage reaction polymerization liquid;
injecting the first-stage reaction polymerization liquid into a second reaction kettle, adjusting the pressure and the temperature of the second reaction kettle, intermittently adding an initiator and a reaction solvent, and controlling the conversion rate of a vinyl acetate monomer to be 30-90% to obtain a second-stage reaction polymerization liquid;
adding a polymerization inhibitor into the second-stage reaction polymerization liquid to terminate the reaction, and cooling and collecting the polymerization liquid;
and (3) carrying out reduced pressure distillation, saponification reaction and precipitation and cleaning treatment on the polymerization solution in sequence to obtain the finished product of the polyethylene-vinyl alcohol resin.
2. The method for preparing a polyethylene-vinyl alcohol resin according to claim 1, wherein the first reaction vessel and the second reaction vessel are both fully mixed flow reaction vessels, and a pressure reducing valve is installed on each of the first reaction vessel and the second reaction vessel.
3. The method for preparing a polyethylene-vinyl alcohol resin according to claim 1, wherein the first reaction vessel and the second reaction vessel are continuously fed, and the pressure of the high-pressure mixer is 2 to 8Mpa.
4. The method for preparing polyethylene-vinyl alcohol resin according to claim 1, wherein the pressure of the first reaction vessel is 2 to 8MPa, the temperature is 50 to 90 ℃, and the residence time is 0.5 to 5 hours; the pressure of the second reaction kettle is 1-7MPa, the temperature is 40-100 ℃, and the retention time is 1-5h.
5. The method for preparing a polyethylene-vinyl alcohol resin according to claim 4, wherein the pressure of the first reaction vessel is 3 to 7MPa, the temperature is 50 to 80 ℃, and the residence time is 0.5 to 3 hours; the pressure of the second reaction kettle is 2-6MPa, the temperature is 50-80 ℃, and the retention time is 1-3h.
6. The method for preparing a polyethylene-vinyl alcohol resin according to claim 1, wherein the initiator is selected from azo initiators or peroxide initiators, and the reaction solvent is methanol or a mixture of methanol and an alcohol solvent having 2 to 4 carbon atoms, wherein the mixture contains 50 to 98% of methanol and 2 to 50% of an alcohol solvent having 2 to 4 carbon atoms.
7. The method for preparing polyethylene-vinyl alcohol resin according to claim 1, wherein the first reaction vessel and the second reaction vessel are washed with methanol 1-3 times before the start of the reaction, then purged with nitrogen for 5-15min, and then vacuum-pumped to the pressure of-0.08 to-0.1 MPa in the first reaction vessel and the second reaction vessel, and finally replaced with ethylene gas 1-2 times.
8. The method for producing a polyethylene-vinyl alcohol resin according to claim 1, wherein the termination reaction is: inputting the second-stage reaction polymerization liquid into a buffer tank, starting a high-pressure pump to inject a polymerization inhibitor solution into the second-stage reaction polymerization liquid, metering the mass of the liquid inlet, stopping the reaction, slowly adjusting a pressure reducing valve until gas is discharged when the temperature of the buffer tank is reduced to below 25 ℃, adjusting the pressure reducing valve in a gradient manner until the pressure of the buffer tank is 0Mpa, and collecting the polymerization liquid.
9. The method for producing a polyethylene-vinyl alcohol resin according to claim 1, wherein the distillation under reduced pressure is: continuously adding methanol or methanol steam into the polymerization solution to remove unreacted vinyl acetate monomer, and ensuring that the content of vinyl acetate in the polymer is lower than 100ppm;
the saponification reaction comprises the following steps: adding 1-20% alkaline methanol solution into 5-35% solid content polymer solution, continuously adding methanol or methanol vapor, timely discharging generated methyl acetate, and adding a certain amount of acetic acid into a reaction system after the reaction is finished to adjust the pH of the solution to 5 to obtain an alcoholysis solution;
the precipitation cleaning treatment comprises the following steps: and (3) separating out the alcoholysis solution in 4-12 times of cold water, then washing for 2-3 times by using the same amount of water separated out, and drying the washed polymer in a vacuum oven at 60-100 ℃ for 2-8h to obtain the polyethylene-vinyl alcohol resin finished product.
10. A polymerization apparatus for preparing the polyethylene vinyl alcohol resin according to any one of claims 1 to 9, comprising:
a high-pressure mixer used for uniformly mixing the vinyl acetate, the initiator and the reaction solvent,
a feed inlet of the first reaction kettle is connected with a discharge outlet of the high-pressure mixer and is used for preparing first-stage reaction polymerization liquid,
a second reaction vessel having a feed inlet connected to the discharge outlet of the first reaction vessel for preparing a second-stage reaction polymerization solution, and
a feed inlet of the buffer tank is connected with a discharge outlet at the bottom of the second reaction kettle and is used for carrying out termination reaction on the second-stage reaction polymerization liquid;
the pressure reducing valves are installed on the first reaction kettle and the second reaction kettle, and a high-pressure pump is arranged on a pipeline between the discharge port of the first reaction kettle and the second reaction kettle.
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