CN112142900A

CN112142900A - Preparation method of styrene-acrylonitrile copolymer

Info

Publication number: CN112142900A
Application number: CN202011072014.6A
Authority: CN
Inventors: 刘波; 刘铭; 孟磊; 孙一峰
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2020-10-09
Filing date: 2020-10-09
Publication date: 2020-12-29
Anticipated expiration: 2040-10-09
Also published as: CN112142900B

Abstract

The invention discloses a preparation method of styrene-acrylonitrile copolymer, which adopts a full mixed flow reactor and a plug flow reactor to be matched for use, and adds an initiator and an incompatible auxiliary agent in the polymerization process, so that toluene or ethylbenzene solvents are not added in the polymerization stage, and the problems of solvent residue and energy consumption caused by the use of the solvents are reduced.

Description

Preparation method of styrene-acrylonitrile copolymer

Technical Field

The invention relates to the field of styrene-acrylonitrile copolymers, in particular to a preparation method of a styrene-acrylonitrile copolymer with low residue and high conversion rate.

Background

An acrylonitrile-styrene copolymer (also called SAN resin or AS resin) is a high molecular polymer formed by radical polymerization reaction of styrene and acrylonitrile AS main raw materials. The SAN resin can be used as a transparent material alone, can also be mixed with high rubber powder to prepare ABS products through extrusion, and can be widely used in industries such as household appliances, automobile manufacturing, instrument fittings, building materials, daily necessities and the like, such as high-grade lamps, tape cassettes, instrument covers, decorative plates, automobile tail lamps, refrigerator storage boxes and the like. SAN resins have excellent processability and can be molded by injection molding, extrusion, blow molding, and the like.

Most of the SAN resins are produced by continuous bulk polymerization (CN201210173350.9, CN201310552143.9, CN98814362.3 and CN201110179219.9) using styrene and acrylonitrile as monomers and adding a small amount of solvent to carry out polymerization. Controlling a certain monomer conversion rate, devolatilizing the slurry under the conditions of high temperature and vacuum to obtain the styrene-acrylonitrile copolymer resin, and condensing unreacted monomers and solvents for recycling.

In the presently disclosed SAN preparation method, a fully mixed flow reactor is generally used for polymerization, which may be a single reactor or a double reactor connected in series or a double reactor connected in parallel, in order to reduce the viscosity of slurry in the polymerization process and facilitate mass and heat transfer, a toluene or ethylbenzene solvent which accounts for 10-20% of the total mass of the reaction liquid is usually added in the polymerization process, however, the added solvent needs to be removed from the slurry in the devolatilization stage, and a large amount of energy is consumed for the removal and cooling recovery of the solvent. However, if no solvent is added, the conversion rate of the monomer is generally not very high, and if the conversion rate is higher than 70%, the viscosity of the reaction solution is too high, and the mass transfer and heat transfer are not easy to control.

In the existing SAN preparation technology, no matter a solvent is added or no solvent is added, volatile matters with the weight percent of more than 30 percent are generally removed after the reaction is finished, so that a large amount of energy is consumed in the devolatilization stage, and simultaneously, the problem of residual monomers or solvents in resin products is also brought.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a preparation method of a styrene-acrylonitrile copolymer, wherein a toluene or ethylbenzene solvent is not added in the polymerization stage, and a pure monomer bulk polymerization mode is adopted, so that the problems of solvent residue and energy consumption caused by the use of the solvent are reduced.

Specifically, the invention provides a preparation method of a styrene-acrylonitrile copolymer, which comprises the following steps:

s1: mixing a styrene monomer, an acrylonitrile monomer and a chain transfer agent to obtain a monomer mixed solution;

s2: adding the monomer mixed solution obtained in the step S1 into a first reactor, and carrying out polymerization reaction at the temperature of 145-165 ℃ and under the residence time of 0.5-3h to obtain slurry A; continuously adding the slurry A into a second reactor, and carrying out polymerization reaction at the temperature of 145-165 ℃ for 0.5-3h to obtain slurry B;

s3: adding an initiator and an auxiliary agent incompatible with the styrene-acrylonitrile copolymer into the slurry B obtained in the step S2, uniformly mixing the initiator and the auxiliary agent by a static mixer, and conveying the mixture into the plug flow reactor; the plug flow reactor is divided into three sections, the temperature of the first section is 150-; the second-stage temperature is 170-210 ℃, and the retention time is 1-30 min; the temperature of the third section is 190 ℃ and 250 ℃, and the retention time is 1-30 min; reacting in a plug flow reactor to obtain slurry C;

s4: continuously feeding the slurry C obtained in the step S3 into a devolatilizer to remove unreacted monomers; and extruding and pelletizing the devolatilized melt to obtain the styrene-acrylonitrile copolymer.

In the present invention, the first reactor and the second reactor are all mixed flow reactors, and preferably, the first reactor and the second reactor are connected in series.

In the invention, the polymerization reaction is carried out in three stages, wherein the first stage and the second stage adopt a full mixed flow reactor, and two full mixed flow reactors are connected in series. In the full mixed flow reactor, a kettle top gas phase condensation pipeline is arranged, so that heat can be transferred through gas phase condensation of monomers, and the temperature in the kettle is further controlled to be stable. The third stage reaction is a plug flow reactor which can be a single-tube or a tubular plug flow reactor, and preferably, a member with a mixing function is arranged in the middle of the tube so as to enhance the mass transfer and the heat transfer of the slurry in the reactor.

In the present invention, the conversion rate of the monomer mixed solution after the reaction in the first reactor is 40 to 55%, the conversion rate of the monomer mixed solution after the reaction in the first reactor is 60 to 75%, and the conversion rate after the reaction in the plug flow reactor is 80% or more, preferably 85% or more.

In order to better achieve the effect of the present invention, the process conditions of each stage of the reaction, including reaction temperature, residence time and outlet conversion, need to be well controlled. Preferably, the temperature of the first reactor is 150-160 ℃, the retention time is 1-2h, and the outlet conversion rate is 45-50%. The temperature of the second reactor is 150-. When the reaction temperature is too high and the residence time is too long, the conversion rate at the outlet of the reaction kettle is high, the viscosity of slurry is too high, the mass transfer and heat transfer in the reactor are difficult, and the final application performance of the product is influenced.

In order to better control the temperature and promote the increase of the conversion rate of the polymerization reaction, the temperature control is required to be carried out in a segmented mode in the third stage of plug flow reactor. Preferably, the temperature is controlled in three stages, with the temperature being gradually increased from the first stage to the third stage. The self-heating can be carried out by fully utilizing the polymerization heat in the plug flow reactor. The plug flow reactor not only plays the role of a polymerization reactor, but also can be used as a preheater for heating slurry to improve the supersaturation degree of the slurry. Compared with the traditional preheater, the invention can reduce the energy consumption of the slurry heating process to the maximum extent. The first period of residence time in the plug flow reactor is preferably 5-15min, and the outlet temperature is preferably 170-180 ℃; the second-stage residence time is preferably 5-10min, and the outlet temperature is preferably 190-; the residence time in the third stage is preferably 5-10min, and the outlet temperature is preferably 220-230 ℃. When the temperature in each stage of the plug flow reactor is too low or the residence time is too short, the slurry temperature and the conversion rate cannot be effectively increased, and the effect of the present invention cannot be well exerted. When the temperature in each section of the plug flow reactor is too high or the residence time is too long, the side reaction degree of the slurry is increased, and the color of the final product is affected.

In the third section of the plug flow reactor, the monomer concentration is low, the reaction temperature is high, and compared with the first section of the full mixed flow reactor and the second section of the full mixed flow reactor, the problems of low reaction rate and low polymer molecular weight exist. In order to promote the further reaction of the monomers in the third stage plug flow reactor, the initiator is supplemented into the slurry B and is uniformly mixed by a static mixer. The added initiator comprises more than two initiators with different activities, the initiators can be azo compounds or peroxides or other initiators known in the art for the polymerization reaction, preferably a combination of more than two organic peroxides, and preferably the initiator comprises an initiator A and an initiator B, wherein the half life of the initiator A at 170 ℃ is 0.5-10min, preferably 1-5 min. The half-life of the initiator B at 190 ℃ is 0.5-10min, preferably 1-5 min. The half-life period of the initiator is controlled in a set range, so that the polymerization reaction rate and the efficiency of the initiator are improved. Preferably, the initiator includes two or more of tert-butyl peroxybenzoate, dicumyl peroxide, di- (tert-butylperoxyisopropyl) benzene, 2, 5-dimethyl-2, 5-bis- (tert-butylperoxy) hexane, tert-butylperoxycumene, di-tert-butylperoxide, cumyl hydroperoxide, and 1,1,3, 3-tetramethylbutyl hydroperoxide. The addition amount of the initiator A is 10-100ppm, preferably 20-50ppm based on the mass of the slurry B; the amount of initiator B added is from 10 to 100ppm, preferably from 20 to 50ppm, based on the mass of the slurry B. When the addition amount of the initiator is too small, the further improvement of the monomer conversion rate is not facilitated; when the amount of the initiator added is too large, the molecular weight of the newly formed polymer is too low, and the properties of the final product are affected.

And an auxiliary agent incompatible with the styrene-acrylonitrile copolymer is also added into the slurry B, so that the molecular weight of the copolymer can be effectively controlled, and the molecular weight of the polymer formed in the third section of plug flow reactor is close to that of the polymer formed in the first section of full mixed flow reactor and the second section of full mixed flow reactor. From the viewpoint of achieving the effect of the invention, the incompatible auxiliary is preferably an alcohol substance having a Hansen solubility parameter of not less than 11, including but not limited to methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol. It was found that when an organic substance having a specific solubility parameter range is added to the reaction solution in the third stage, the progress of the polymerization reaction and the increase in the molecular weight of the polymer can be promoted. From the analysis of mechanism, it is probably because the viscosity of the reaction solution in the third stage is very high, when the organic matter incompatible with the styrene-acrylonitrile copolymer is added, the gel effect of the reaction system is strengthened, the termination of the polymerization reaction is inhibited, and the reaction rate and the molecular weight are increased simultaneously. To further achieve the effects of the present invention, the incompatible auxiliary is preferably an alcohol having a Hansen solubility parameter of not less than 12. Since the added incompatible auxiliary needs to be removed in the devolatilization stage, it is preferred that the incompatible auxiliary has a boiling point below 100 c, preferably below 80 c, in order to reduce residues in the resin product.

Specifically, the incompatible material of the present invention is preferably methanol or ethanol, more preferably methanol.

The amount of the incompatible auxiliary added is 2 to 10 parts by mass, preferably 4 to 6 parts by mass, based on 100 parts by mass of the slurry B. When the amount is too small, the effect of improving the reaction rate and molecular weight in the third reaction stage is not significant. When the amount is too high, the productivity is not improved.

In the invention, the monomer mixed solution is added with the following components in parts by mass:

60-85 parts by mass of styrene monomer,

15-40 parts by mass of acrylonitrile-based monomer,

0.05-0.3 part by mass of a chain transfer agent.

The styrene monomer of the invention can be styrene or alpha-methyl styrene, and is preferably styrene. The acrylonitrile-based monomer may be acrylonitrile or methacrylonitrile, and is preferably acrylonitrile.

In the preparation method provided by the invention, the monomer mixed solution is added with the chain transfer agent besides the two monomers of styrene and acrylonitrile so as to control the molecular weight of the polymer within a certain range. In some preferred embodiments, the chain transfer agent added is a mercaptan type chain transfer agent, such as tertiary dodecyl mercaptan, which has a better chain transfer capability with respect to both styrene and acrylonitrile monomers. In some more preferred embodiments, the amount of the chain transfer agent added is preferably 0.05 to 0.2 wt% of the total amount of monomers, based on the total mass of monomers in the mixed raw materials, in order to control the weight average molecular weight of the copolymer to be in the range of 8 to 20 ten thousand.

In the preparation method provided by the invention, after the polymerization reaction is finished, the obtained slurry is subjected to devolatilization treatment to remove volatile components in the slurry, wherein the volatile components comprise styrene monomers, acrylonitrile monomers, incompatible auxiliaries, oligomers, accumulated organic impurities in a reactor and the like. The devolatilization process may be any devolatilization process used in conventional styrene and acrylonitrile copolymerization processes, such as one-stage or multi-stage devolatilization. The alternative devolatilizer may be one or a combination of flash tank, falling film devolatilizer, scraped devolatilizer, twin screw extruder, twin screw devolatilizer. The falling strand devolatilizer is preferably used from the viewpoint of both productivity and cost.

The top of the devolatilizer is provided with a preheater which is needed to preheat the slurry coming out of the polymerizer to the devolatilization temperature so as to improve the supersaturation degree of the slurry. The melt temperature of the devolatilization unit is generally controlled to be 180 ℃ to 250 ℃, preferably 210 ℃ to 230 ℃. The absolute pressure in the devolatilizer is controlled to be within 5KPa, preferably within 2 KPa. The volatile components after devolatilization are mainly unreacted monomers, and are recycled after being condensed by a low-temperature refrigerant. The total residual content of the resin of the invention after devolatilization can be less than 1000 ppm.

In the preparation method provided by the invention, any type of auxiliary agent with any content commonly used in the field can be added in the process according to the required copolymer performance, including but not limited to a release agent, an ultraviolet absorbent, an antioxidant, a coloring agent and the like.

By controlling the process conditions, the prepared styrene-acrylonitrile copolymer has good mechanical properties (such as tensile strength, bending strength, impact strength and the like) and good optical properties.

Therefore, the invention also provides a styrene-acrylonitrile copolymer prepared by the preparation method of any one of the technical schemes.

In the styrene-acrylonitrile copolymer provided by the invention, the acrylonitrile content in the finally obtained copolymer can be changed according to the addition amount of the acrylonitrile monomer. In some preferred embodiments, the styrene-acrylonitrile copolymer provided by the invention has an acrylonitrile content of 10 to 35 wt%; more preferably, the acrylonitrile content is 20 to 30 wt%. The styrene-acrylonitrile copolymer provided by the invention can be prepared into common products in any form and any type according to a common processing and forming process, can be suitable for any common application field or application occasion, and is particularly suitable for application fields such as cosmetic packaging, food containers, refrigerator fresh-keeping boxes, dust covers, lighters, transparent parts of household appliances and the like.

Compared with the conventional process, the preparation method of the styrene-acrylonitrile copolymer provided by the invention has the advantages of higher conversion rate, lower comprehensive energy consumption in the devolatilization stage and lower residual of the obtained product. The preparation method has simple and convenient process, does not need complex equipment, and is very suitable for large-scale industrial production.

Drawings

FIG. 1 is a schematic view of a system for producing a styrene-acrylonitrile copolymer according to an embodiment of the present invention;

wherein R101 is a first reactor, R102 is a second reactor, R103 is a plug flow reactor, and D101 is a devolatilizer.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following specific examples.

In the examples of the present invention and the comparative examples, the sources of the raw materials are shown in table 1.

Table 1 raw material source information

Name of raw materials	For short	Rank of	Suppliers of goods
				Styrene (meth) acrylic acid ester	SM	Industrial grade	Qilu petrochemical
Acrylonitrile	AN	Industrial grade	Jilin petrochemical
				Tert-dodecyl mercaptan	t-DDM	Industrial grade	Chevrolet dragon
Di-tert-butyl peroxide	DTBP	Industrial grade	Akema
				Cumene hydroperoxide	CHP	Industrial grade	Akema
Methanol	/	Reagent grade	Koimeu tea
				Ethanol	/	Reagent grade	Koimeu tea
Tetrahydrofuran (THF)	THF	Reagent grade	Koimeu tea

In the examples and comparative examples of the present invention, the first reactor and the second reactor were all a total mixed flow reactor.

In the examples and comparative examples of the present invention, the methods for measuring the molecular weight, solid content and monomer conversion of the polymer were as follows:

molecular weight measurement

The molecular weight was measured by liquid gel chromatography (GPC), mobile phase Tetrahydrofuran (THF), detector using a parallax refractometer, and monodisperse polystyrene as a standard.

Resin content (conversion) test

The resin content was tested by sampling from the reactor outlet by a sampler, respectively. The test method is as follows: weighing 1g of reaction solution, placing the reaction solution in tin foil paper (the tin foil paper is weighed in advance), placing the tin foil paper in a vacuum oven at 160 ℃, controlling the absolute pressure to be less than 1KPa, vacuumizing for 0.5h, taking out the tin foil paper, cooling the tin foil paper at room temperature, and weighing the dried dry base resin. The resin content can be calculated by dividing the mass of the dry resin by the mass of the reaction solution. Resin content was repeated three times per sample and averaged.

The polymer properties were measured as shown in Table 2.

TABLE 2 Polymer Performance test standards and conditions

Test items	Test standard	Test conditions
			Melt Flow Rate (MFR)	ISO 1133	220℃，10KG
Tensile strength	ISO 527	1A/5
			Elongation at break	ISO 527	1A/5
Bending strength	ISO 527	1A/5

Example 1

80Kg of Styrene (SM), 20Kg of Acrylonitrile (AN) and 0.1Kg of tertiary dodecyl mercaptan as a chain transfer agent were added to a 200L compounding tank and mixed well.

Referring to fig. 1, the above raw material mixture was continuously fed into a first reactor R101 having a volume of 30L at a feed rate of 10L/h, and the temperature of R101 was maintained at about 160 ℃ by adjusting the amount of gas phase condensate reflux, and the average residence time of the material in R101 was 1.0h, thereby obtaining a slurry a. The monomer conversion of slurry a was tested to be 50%.

Continuously conveying the slurry A into a fully-mixed flow polymerization kettle R102 with the volume of 30L and good heat preservation at the feeding speed of 10L/h, controlling the temperature of the R102 to be about 160 ℃ by adjusting the gas phase condensation reflux quantity, and controlling the average residence time of the material in the R101 to be 1.0h to obtain the slurry B. The monomer conversion of slurry B was tested to be 70%.

Slurry B was continuously fed to the latter stage, and a composition comprising 45ppm of di-tert-butyl peroxide (based on the mass of slurry B), 45ppm of cumene hydroperoxide (based on the mass of slurry B), and 5 wt% of methanol (Hansen solubility parameter 14.5, boiling point 64.7 ℃ C., added amount based on the mass of slurry B) was added to slurry B, and the mixture was uniformly mixed by a static mixer and then fed into an axial flow reactor R103. The jacket of the plug flow reactor R103 is filled with oil bath and is divided into three sections for temperature control, wherein the temperature of the jacket of the first section is 170 ℃, the material retention time is 10min, the temperature of the jacket of the second section is 190 ℃, the material retention time is 8min, the temperature of the jacket of the third section is 225 ℃, and the material retention time is 7 min. The outlet slurry C monomer conversion was 87%.

Feeding the slurry C into a falling strip devolatilizer D101, controlling the temperature of the melt in the devolatilizer to be 220 ℃ and the pressure to be 1.5 KPa. And water-cooling and pelletizing the devolatilized polymer melt to obtain a granular SAN product. The tested resin always remained 905 ppm. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Example 2

74Kg of Styrene (SM), 26Kg of Acrylonitrile (AN) and 0.2Kg of chain transfer agent tert-dodecyl mercaptan were added to a 200L compounding tank and mixed well.

Continuously conveying the raw material mixed liquor into a first reactor R101 with the volume of 30L at the feeding speed of 10L/h, controlling the temperature of the R101 to be about 153 ℃ by adjusting the gas phase condensation reflux quantity, and controlling the average residence time of the materials in the R101 to be 1.5h to obtain slurry A. The monomer conversion at one stage was tested to be 50%.

Continuously conveying the slurry A into a fully-mixed flow polymerization kettle R102 with the volume of 30L and good heat preservation at the feeding speed of 10L/h, controlling the temperature of the R102 to be about 153 ℃ by adjusting the gas phase condensation reflux quantity, and controlling the average residence time of the materials in the R101 to be 1.5h to obtain the slurry B. The monomer conversion for the second stage reaction was tested to be 68%.

Slurry B was continuously fed to the latter stage, and a composition comprising 45ppm of di-tert-butyl peroxide (based on the mass of slurry B), 45ppm of cumene hydroperoxide (based on the mass of slurry B), and 5 wt% of methanol (Hansen solubility parameter 14.5, boiling point 64.7 ℃ C., added amount based on the mass of slurry B) was added to slurry B, and the mixture was uniformly mixed by static mixer 6 and fed into plug flow reactor R103. The jacket of the plug flow reactor R103 is filled with oil bath and is divided into three sections for temperature control, wherein the temperature of the jacket of the first section is 170 ℃, the material retention time is 10min, the temperature of the jacket of the second section is 190 ℃, the material retention time is 8min, the temperature of the jacket of the third section is 225 ℃, and the material retention time is 7 min. The outlet slurry C monomer conversion was 89%.

Feeding the slurry C into a falling strip devolatilizer D101, controlling the temperature of the melt in the devolatilizer to be 220 ℃ and the pressure to be 1.5 KPa. And water-cooling and pelletizing the devolatilized polymer melt to obtain a granular SAN product. The total residual resin tested was 725 ppm. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Example 3

74Kg of Styrene (SM), 26Kg of Acrylonitrile (AN) and 0.1Kg of chain transfer agent tert-dodecyl mercaptan were added to a 200L compounding tank and mixed well.

Continuously conveying the raw material mixed liquid into a 30L fully-mixed flow polymerization kettle R101 at a feeding speed of 10L/h, controlling the temperature of the R101 to be about 165 ℃ by adjusting the gas-phase condensation reflux quantity, and controlling the average retention time of the materials in the R101 to be 45min to obtain slurry A. The monomer conversion for one stage was tested to be 53%.

Continuously conveying the slurry A into a fully-mixed flow polymerization kettle R102 with the volume of 30L and good heat preservation at the feeding speed of 10L/h, controlling the temperature of the R102 to be about 165 ℃ by adjusting the gas phase condensation reflux quantity, and controlling the average residence time of the materials in the R101 to be 45min to obtain the slurry B. The monomer conversion for the second stage reaction was tested to be 73%.

Slurry B was continuously fed to the latter stage, and a composition comprising 20ppm of di-tert-butyl peroxide (based on the mass of slurry B), 85ppm of cumene hydroperoxide (based on the mass of slurry B), and 3 wt% of methanol (Hansen solubility parameter 14.5, boiling point 64.7 ℃ C., added amount based on the mass of slurry B) was added to slurry B, and the mixture was uniformly mixed by static mixer 6 and fed into plug flow reactor R103. The jacket of the plug flow reactor R103 is filled with oil bath and is divided into three sections for temperature control, wherein the temperature of the jacket of the first section is 180 ℃, the material retention time is 5min, the temperature of the jacket of the second section is 200 ℃, the material retention time is 15min, the temperature of the jacket of the third section is 230 ℃, and the material retention time is 10 min. The outlet slurry C monomer conversion was 93%.

Feeding the slurry C into a falling strip devolatilizer D101, controlling the temperature of the melt in the devolatilizer to be 210 ℃ and the pressure to be 1.0 KPa. And water-cooling and pelletizing the devolatilized polymer melt to obtain a granular SAN product. The total residual resin tested was 527 ppm. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Example 4

60Kg of Styrene (SM), 40Kg of Acrylonitrile (AN) and 0.2Kg of tertiary dodecyl mercaptan as a chain transfer agent were put into a 200L compounding tank 1 and mixed well.

Continuously conveying the raw material mixed liquid into a 30L fully-mixed flow polymerization kettle R101 at a feeding speed of 10L/h, controlling the temperature of the R101 to be kept at about 145 ℃ by adjusting the gas phase condensation reflux quantity, and controlling the average residence time of the materials in the R101 to be 2.5h to obtain slurry A. The monomer conversion for one stage was tested to be 42%.

The slurry A is continuously conveyed into a fully-mixed flow polymerization kettle R102 with the volume of 30L and good heat preservation at the feeding speed of 10L/h, the temperature of the R102 is controlled to be kept at about 145 ℃ by adjusting the gas phase condensation reflux quantity, and the average residence time of the materials in the R101 is 2.5h, so that the slurry B is obtained. The monomer conversion for the second stage reaction was tested to be 61%.

The slurry B was continuously fed to the latter stage, and a composition comprising 85ppm of di-tert-butyl peroxide (based on the mass of the slurry B), 20ppm of cumene hydroperoxide (based on the mass of the slurry B), and 8 wt% of ethanol (Hansen solubility parameter 12.7, boiling point 78 ℃ C., addition amount based on the mass of the slurry B) was added to the slurry B, and the mixture was uniformly mixed by a static mixer 6 and fed into an axial flow reactor R103. The jacket of the plug flow reactor R103 is filled with oil bath and is divided into three sections for temperature control, wherein the temperature of the jacket of the first section is 165 ℃, the material retention time is 8min, the temperature of the jacket of the second section is 185 ℃, the material retention time is 7min, the temperature of the jacket of the third section is 230 ℃, and the material retention time is 7 min. The outlet slurry C monomer conversion was 85%.

Feeding the slurry C into a falling strip devolatilizer D101, controlling the temperature of the melt in the devolatilizer to be 225 ℃ and the pressure to be 1.5 KPa. And water-cooling and pelletizing the devolatilized polymer melt to obtain a granular SAN product. The total residual resin tested was 989 ppm. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Comparative example 1

Comparative example 1 contrasts with example 2, except that no initiator and incompatible co-agent methanol were added during the third stage of polymerization, and the process conditions were otherwise identical. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Comparative example 2

Comparative example 2 compares to example 2 and the process conditions are identical for the formulations except that no initiator is added during the third stage of polymerization. The structure and performance test results of styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3

Comparative example 3

Comparative example 3 contrasts with example 2, except that the incompatible auxiliary methanol was not added during the third stage polymerization, and the process conditions were otherwise identical. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

Comparative example 4

Comparative example 4 is compared with example 2, except that tetrahydrofuran (Hansen solubility parameter 9.5, boiling point 66 ℃) which is a good solvent for styrene-acrylonitrile copolymer of the same quality as methanol is added during the third polymerization stage, and the process conditions of the formulation are completely the same. The structure and performance test results of the styrene-acrylonitrile copolymer (SAN resin) are shown in Table 3.

TABLE 3 comparison of the Properties of the examples and comparative formulations

As can be seen from examples 1 to 4, when the polymerization was carried out in three stages and an initiator having a specific structure and an auxiliary incompatible with the styrene-acrylonitrile copolymer were added to the third stage polymerization in accordance with the requirements of the invention, the styrene-acrylonitrile polymer obtained by the present invention had a high conversion rate, low resin residue after devolatilization, and good mechanical properties.

As can be seen from the comparison of example 2 with comparative examples 1 to 3, the third polymerization stage requires the simultaneous addition of an initiator and an auxiliary incompatible with the styrene-acrylonitrile copolymer. When the initiator is not added, the conversion of the polymerization reaction is difficult to be further improved, and the resin residue after devolatilization is high. When only the initiator is added without the addition of the styrene-acrylonitrile copolymer incompatible auxiliary required by the present invention, the degree of improvement of the polymerization conversion is limited, and the molecular weight distribution of the final product is broad and the mechanical properties are significantly reduced.

As can be seen from the comparison of example 2 and comparative example 4, only incompatible auxiliaries within a specific solubility parameter range can be added to the third polymerization stage to achieve the beneficial effects of the invention.

Claims

1. A preparation method of styrene-acrylonitrile copolymer is characterized by comprising the following steps:

s2: adding the monomer mixed solution of S1 into a first reactor, and carrying out polymerization reaction at the temperature of 145-165 ℃ and under the residence time of 0.5-3h to obtain slurry A; adding the slurry A into a second reactor, and carrying out polymerization reaction at the temperature of 145-165 ℃ for 0.5-3h to obtain slurry B;

s3: adding an initiator and an auxiliary agent incompatible with the styrene-acrylonitrile copolymer into the slurry B obtained in the step S2, uniformly mixing the initiator and the auxiliary agent by a static mixer, and conveying the mixture into the plug flow reactor; the plug flow reactor is divided into three sections; the first-stage temperature is 150 ℃ and 190 ℃, and the retention time is 1-30 min; the second-stage temperature is 170-210 ℃, and the retention time is 1-30 min; the temperature of the third section is 190 ℃ and 250 ℃, and the retention time is 1-30 min; reacting in a plug flow reactor to obtain slurry C;

2. The method for preparing styrene-acrylonitrile copolymer according to claim 1, wherein the first reactor and the second reactor are a complete mixed flow reactor; preferably, the first reactor and the second reactor are connected in series.

3. The method for preparing styrene-acrylonitrile copolymer as claimed in claim 1, wherein the first reactor temperature is 150-; the temperature of the second reactor is 150-160 ℃, the retention time is 1-2h, and the outlet conversion rate is 60-75 wt%, preferably 65-70 wt%.

4. The method for preparing styrene-acrylonitrile copolymer as claimed in claim 1, wherein the first residence time in the plug flow reactor is 5-15min, the outlet temperature is 170-180 ℃; the residence time of the second section is 5-10min, and the outlet temperature is 190-; the residence time of the third section is 5-10min, and the outlet temperature is 220-230 ℃.

5. The method for preparing styrene-acrylonitrile copolymer according to claim 1, wherein the initiator in step S3 comprises two or more initiators with different activities, and the initiator can be azo compound or peroxide or other initiators known in the art for such polymerization reaction, preferably a combination of two or more organic peroxides,

preferably, the initiator comprises an initiator A and an initiator B, wherein the half-life period of the initiator A at 170 ℃ is 0.5-10min, preferably 1-5min, and the half-life period of the initiator B at 190 ℃ is 0.5-10min, preferably 1-5 min.

6. The process according to claim 5, wherein the initiator A is added in an amount of 10 to 100ppm, preferably 20 to 50ppm, based on the mass of the slurry B; the amount of initiator B added is from 10 to 100ppm, preferably from 20 to 50ppm, based on the mass of the slurry B.

7. The method according to claim 1, wherein an auxiliary incompatible with the styrene-acrylonitrile copolymer is added in step S3, and the auxiliary incompatible with the styrene-acrylonitrile copolymer is an alcohol having Hansen solubility parameter of not less than 11, preferably an alcohol having Hansen solubility parameter of not less than 12 and boiling point of not more than 80 ℃;

preferably, the styrene-acrylonitrile copolymer incompatible auxiliary is methanol, ethanol, n-propanol, isopropanol, n-butanol or isobutanol, more preferably methanol or ethanol.

8. The method for producing a styrene-acrylonitrile copolymer according to claim 1, wherein the incompatible auxiliary is added in an amount of 2 to 10 parts by mass, preferably 4 to 6 parts by mass, based on 100 parts by mass of the slurry B.

9. The method for producing a styrene-acrylonitrile copolymer according to claim 1, wherein the monomer mixture is added with the following components in parts by mass:

60-85 parts by mass of styrene monomer,

15-40 parts by mass of acrylonitrile-based monomer,

0.05-0.3 mass part of chain transfer agent;

the styrene monomer is styrene or alpha-methyl styrene, preferably styrene; the acrylonitrile-based monomer is acrylonitrile or methacrylonitrile, and acrylonitrile is preferred.

10. The method for preparing styrene-acrylonitrile copolymer as claimed in claim 1, wherein the temperature in the devolatilizer is 180-250 ℃, preferably 210-230 ℃; the devolatilizer absolute pressure is below 5KPa, preferably below 2 KPa.