An ethylene-vinyl acetate copolymer and a production method thereof

Abstract

The present invention discloses an ethylene-vinyl acetate copolymer and a production method thereof. The production method uses ethylene and vinyl acetate as raw materials and sequentially includes compression, polymerization, high-pressure separation, low-pressure separation, granulation and degassing processes. During the low-pressure separation process, the pressure is 43-48 kPa. By optimizing the pressure of the low-pressure separation, the present invention can significantly reduce the volatile content in the prepared ethylene-vinyl acetate copolymer while reducing energy consumption and material consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical production, and particularly to an ethylene-vinyl acetate copolymer and a production method thereof. Background Art

[0002] Ethylene-vinyl acetate copolymer (EVA), also known as ethylene-vinyl acetate copolymer, is prepared by copolymerizing ethylene (E) and vinyl acetate (VA), and is the most important product among ethylene copolymers.

[0003] Generally speaking, the production process of EVA products is mainly divided into compression, polymerization reaction, and product separation. The melt generated after the polymerization reaction enters the high-pressure separation system, and through cooling and pressure reduction, ethylene in the melt is initially separated; then it enters the low-pressure separation system, and through further cooling and pressure reduction, ethylene and vinyl acetate in the melt are separated. The melt then enters the extruder, is granulated and sent to the degassing silo, and unreacted ethylene or vinyl acetate in the material is removed in the degassing silo to obtain the required EVA product. During the production process of EVA products, some unreacted monomers will dissolve in the polymer matrix as the polymer melt flows. After extrusion granulation, the product contains some unreacted monomers such as ethylene (E) and vinyl acetate (VA) and some moisture, and the sum of these components is the volatile content of the product. The higher the volatile content of the EVA product, the more copolymer monomer odor will be volatilized during the use of the EVA product, and downstream users will be affected by the odor during use, resulting in a decline in product quality, thus affecting the sales of EVA products; at the same time, when there is a large amount of volatile content in the product, the unreacted monomers enter the RTO incineration after being removed by the subsequent degassing process, resulting in an increase in the material consumption of the device and highlighting environmental protection problems. Under the existing production parameter conditions, the volatile content in the EVA product obtained after degassing basically remains at 0.25%-0.35%, with a relatively high content and large energy and material consumption. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an ethylene-vinyl acetate copolymer and a production method thereof, so as to reduce the volatile content in the ethylene-vinyl acetate copolymer obtained after degassing to less than 0.20%, and at the same time achieve energy conservation and consumption reduction.

[0005] In a first aspect, the present invention provides a production method of an ethylene-vinyl acetate copolymer. The production method uses ethylene and vinyl acetate as raw materials, and successively includes compression, polymerization, high-pressure separation, low-pressure separation, granulation, and degassing processes. During the low-pressure separation process, the pressure is 43-48 kPa, preferably 44-46 kPa.

[0006] Optionally, during the low-pressure separation process, the temperature is 183-187 °C, preferably 184-186 °C.

[0007] Optionally, during the high-pressure separation process, the pressure is 20.5 - 21.5 MPa, preferably 20.8 - 21.2 MPa.

[0008] Optionally, during the high-pressure separation process, the temperature is 183 - 190 °C, preferably 183 - 188 °C.

[0009] Optionally, the temperature of the degassing is 22 - 25 °C, preferably 23 - 25 °C.

[0010] Optionally, the duration of the degassing is 35 - 37 h, preferably 35.5 - 36.5 h.

[0011] Optionally, it is compressed to 20 - 260 MPa, preferably 25 - 260 MPa.

[0012] Optionally, the temperature of the polymerization is 200 - 250 °C.

[0013] Optionally, the pressure of the polymerization is 200 - 250 MPa, preferably 210 - 250 MPa.

[0014] In a second aspect, the present application also aims to provide an ethylene-vinyl acetate copolymer prepared by the production method as described above.

[0015] As described above, for the ethylene-vinyl acetate copolymer and its production method of the present invention, by optimizing the pressure and temperature of the low-pressure separation, the pressure and temperature of the high-pressure separation, and the degassing temperature and duration, while reducing material consumption and energy consumption, the content of volatile components in the obtained EVA product is reduced. Specifically:

[0016] (1) By adjusting the pressure and temperature of the low-pressure separation and the pressure and temperature of the high-pressure separation, the present invention can reduce the content of volatile components in the obtained EVA product while reducing material consumption and energy consumption. Among them, without affecting the production operation of the device, reducing the low-pressure separation pressure has the greatest impact on the content of volatile components in the product and the least impact on the production of the device, and it also helps to save energy and reduce consumption.

[0017] (2) By optimizing the degassing temperature and duration, the present invention can reduce the content of volatile components in the obtained EVA product. Among them, the higher the degassing temperature and the longer the degassing time, the more beneficial it is to reduce the content of volatile components in the product. However, too high a degassing temperature will cause the product particles to stick in the silo, affecting the particle transportation, and too long a degassing duration will cause a significant increase in the power consumption of the device. In actual production operation, it is necessary to adjust the degassing temperature and time in combination with the actual production situation and energy consumption situation, so as to effectively reduce the content of volatile components in the obtained EVA product. Detailed implementation manners

[0018] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0019] The present invention provides a method for producing ethylene-vinyl acetate copolymer, comprising:

[0020] Compress ethylene and vinyl acetate to 20 - 260 MPa, then carry out polymerization at 200 - 250 °C and 200 - 250 MPa, then carry out high-pressure separation at 20.5 - 21.5 MPa and 183 - 190 °C, then carry out low-pressure separation at 43 - 48 kPa and 183 - 187 °C, and then carry out degassing at 22 - 25 °C for 35 - 37 h.

[0021] The present invention also provides an ethylene-vinyl acetate copolymer prepared by the production method as described above.

[0022] The following will specifically illustrate the present invention through specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0023] Example 1

[0024] A method for producing an ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0025] S1. Compression: Ethylene gas enters a primary compressor through an ethylene feed pipeline (feed rate: 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into a secondary compressor through a compression pipeline;

[0026] Vinyl acetate (i.e., VA, feed rate: 11 t / h) enters the secondary compressor through a vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa;

[0027] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxy-2-ethylhexanoate in a mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor, and is injected into the four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction starts;

[0028] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the temperature of the first to fourth reactors can be adjusted by regulating the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, wherein the low-pressure hot water temperature is 120 °C and the medium-pressure hot water temperature is 125 °C) to dissipate heat, so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressure of the four reactors is 210 MPa, and the pulse control valve is intermittently opened throughout the reaction, and the opening frequency is 80 s / time;

[0029] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank, and the temperature of the high-pressure separation tank is adjusted to 185 °C and the pressure is 21 MPa;

[0030] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank, and the temperature of the low-pressure separation tank is adjusted to 185 °C and the pressure is 45 kPa;

[0031] S5. Granulation: The melt after low-pressure separation enters the extruder, and the melt is extruded into particles in the extruder to obtain EVA particles;

[0032] S6. Degassing: Subsequently, the EVA particles are sent to the degassing silo and degassed at 25 °C for 36 h to obtain the EVA product.

[0033] Example 2

[0034] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0035] S1. Compression: Ethylene gas enters the primary compressor via the ethylene feed line (feed rate is 20t / h). The primary compressor compresses the ethylene gas to 20MPa. Subsequently, the compressed ethylene gas is sent to the secondary compressor via the compression line;

[0036] Vinyl acetate (VA, feed rate 11t / h) enters the secondary compressor through the VA feed line. In the secondary compressor, VA is mixed with compressed ethylene gas to obtain a mixture, which is then compressed to 220MPa by the secondary compressor.

[0037] S2. polymerization: The mixture compressed to 220 MPa enters the preheater through the communicating pipe between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneoheptanoate, tert-butyl peroxypivalate and tert-butyl peroxy 2-ethylhexanoate in accordance with the mass percentage of 58 wt %: 20 wt %: 10 wt %: 6 wt %: 6 wt %) is injected into the production unit through the initiator injection line connected at the feed port of each reactor and injected into the four reactors at four points (wherein the injection rate of the initiator in the first reactor is 41 kg / h; the injection rate of the initiator in the second reactor is 37 kg / h; the injection rate of the initiator in the third reactor is 32 kg / h; the injection rate of the initiator in the fourth reactor is 27 kg / h). After the initiator is injected, the polymerization reaction is initiated.

[0038] Since the polymerization reaction of ethylene and vinyl acetate is a highly exothermic reaction, the hot water system (a low-pressure hot water station and a medium-pressure hot water station are provided, wherein the low-pressure hot water temperature is 120°C and the medium-pressure hot water temperature is 125°C) can be adjusted to dissipate heat and thus adjust the temperatures of the first to fourth-stage reactors, so that the reaction temperature in the first-stage reactor is 200°C, the reaction temperature in the second-stage reactor is 200°C, the reaction temperature in the third-stage reactor is 210°C, and the reaction temperature in the fourth-stage reactor is 215°C. The pressure of the four reactors is 210 MPa. The pulse control valve is intermittently opened throughout the reaction, with an opening frequency of 80s / time.

[0039] S3 high-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through a connecting pipe between the fourth-stage reactor and the high-pressure separation tank, and the temperature of the high-pressure separation tank is adjusted to 183 ° C and the pressure is 20.5MPa;

[0040] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipe between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 183°C and the pressure is 43kPa.

[0041] S5. Granulation: The melt after low-pressure separation enters the extruder, and the melt is extruded into granular form in the extruder to obtain EVA particles.

[0042] S6. Degassing: Subsequently, the EVA particles are sent to a degassing silo and degassed at a temperature of 22 °C for 36 h to obtain the EVA product.

[0043] That is, the differences between this example and Example 1 are as follows: the temperature of high-pressure separation is 183 °C, the pressure of high-pressure separation is 20.5 MPa, the temperature of low-pressure separation is 183 °C, the pressure of low-pressure separation is 43 kPa, and the degassing temperature is 22 °C.

[0044] Example 3

[0045] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0046] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipeline (feed rate is 20 t / h), and the primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into the secondary compressor through the compression pipeline.

[0047] Vinyl acetate (i.e., VA, feed rate is 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa.

[0048] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxy-2-ethylhexanoate according to the mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor and is injected into the four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction is initiated.

[0049] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the heat can be dissipated by adjusting the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, where the low-pressure hot water temperature is 120°C and the medium-pressure hot water temperature is 125°C), thereby adjusting the temperature of the first to fourth reactors so that the reaction temperature in the first reactor is 200°C, the reaction temperature in the second reactor is 200°C, the reaction temperature in the third reactor is 210°C, and the reaction temperature in the fourth reactor is 215°C. The pressure of the four reactors is 210 MPa, and the pulse control valve is intermittently opened throughout the reaction, with an opening frequency of 80 s / time;

[0050] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. The temperature of the high-pressure separation tank is adjusted to 190°C and the pressure is 21.5 MPa;

[0051] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 187°C and the pressure is 48 kPa;

[0052] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0053] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at 24°C for 36 h to obtain the EVA product.

[0054] That is, the differences between this embodiment and Embodiment 1 are: the temperature of high-pressure separation is 190°C, the pressure of high-pressure separation is 21.5 MPa, the temperature of low-pressure separation is 187°C, the pressure of low-pressure separation is 48 kPa, and the degassing temperature is 24°C.

[0055] Comparative Example 1

[0056] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the embodiment in CN110563871A. The specific steps are as follows:

[0057] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipeline (feed rate is 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into the secondary compressor through the compression pipeline;

[0058] Vinyl acetate (i.e., VA, feed rate is 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa;

[0059] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (which is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneoheptanoate, tert-butyl peroxyneopentanoate, and tert-butyl peroxy-2-ethylhexanoate in a mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor and is injected into the four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction starts;

[0060] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the temperature of the first to fourth reactors can be adjusted by regulating the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, wherein the low-pressure hot water temperature is 120 °C and the medium-pressure hot water temperature is 125 °C) to dissipate heat, so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressure of the four reactors is 210 MPa. The pulse control valve is intermittently opened during the whole reaction process, and the opening frequency is 80 s / time;

[0061] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. The temperature of the high-pressure separation tank is adjusted to 200 °C and the pressure is 24 MPa;

[0062] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 190 °C and the pressure is 80 kPa;

[0063] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0064] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at 25 °C for 36 h to obtain the EVA product.

[0065] That is, the differences between this comparative example and Example 1 are: the temperature of high-pressure separation is 200 °C, the pressure of high-pressure separation is 24 MPa, the temperature of low-pressure separation is 190 °C, and the pressure of low-pressure separation is 80 kPa.

[0066] Comparative Example 2

[0067] A method for producing an ethylene-vinyl acetate copolymer resin is carried out in the production apparatus of the embodiment in CN110563871A, and the specific steps are as follows:

[0068] S1. Compression: Ethylene gas enters the primary compressor via the ethylene feed line (feed rate is 20t / h). The primary compressor compresses the ethylene gas to 20MPa. Subsequently, the compressed ethylene gas is sent to the secondary compressor via the compression line;

[0069] Vinyl acetate (VA, feed rate 11t / h) enters the secondary compressor through the VA feed line. In the secondary compressor, VA is mixed with compressed ethylene gas to obtain a mixture, which is then compressed to 220MPa by the secondary compressor.

[0070] S2. polymerization: The mixture compressed to 220 MPa enters the preheater through the communicating pipe between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneoheptanoate, tert-butyl peroxypivalate and tert-butyl peroxy 2-ethylhexanoate in accordance with the mass percentage of 58 wt %: 20 wt %: 10 wt %: 6 wt %: 6 wt %) is injected into the production unit through the initiator injection line connected at the feed port of each reactor and injected into the four reactors at four points (wherein the injection rate of the initiator in the first reactor is 41 kg / h; the injection rate of the initiator in the second reactor is 37 kg / h; the injection rate of the initiator in the third reactor is 32 kg / h; the injection rate of the initiator in the fourth reactor is 27 kg / h). After the initiator is injected, the polymerization reaction is initiated.

[0071] Since the polymerization reaction of ethylene and vinyl acetate is a highly exothermic reaction, the hot water system (a low-pressure hot water station and a medium-pressure hot water station are provided, wherein the low-pressure hot water temperature is 120°C and the medium-pressure hot water temperature is 125°C) can be adjusted to dissipate heat and thus adjust the temperatures of the first to fourth-stage reactors, so that the reaction temperature in the first-stage reactor is 200°C, the reaction temperature in the second-stage reactor is 200°C, the reaction temperature in the third-stage reactor is 210°C, and the reaction temperature in the fourth-stage reactor is 215°C. The pressure of the four reactors is 210 MPa. The pulse control valve is intermittently opened throughout the reaction, with an opening frequency of 80s / time.

[0072] S3 high-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through a connecting pipe between the fourth-stage reactor and the high-pressure separation tank, and the temperature of the high-pressure separation tank is adjusted to 180 ° C and the pressure is 30MPa;

[0073] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 180 °C and the pressure is 50 kPa.

[0074] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets.

[0075] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at a temperature of 30 °C for 36 h to obtain the EVA product.

[0076] That is, the differences between this comparative example and Example 1 are as follows: the temperature of high-pressure separation is 180 °C, the pressure of high-pressure separation is 30 MPa, the temperature of low-pressure separation is 180 °C, the pressure of low-pressure separation is 50 kPa, and the degassing temperature is 30 °C.

[0077] Comparative Example 3

[0078] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0079] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipeline (feed rate: 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent to the secondary compressor through the compression pipeline.

[0080] Vinyl acetate (i.e., VA, feed rate: 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa.

[0081] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxy-2-ethylhexanoate in a mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor and is injected into four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction is initiated.

[0082] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the heat can be dissipated by adjusting the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, where the low-pressure hot water temperature is 120 °C and the medium-pressure hot water temperature is 125 °C), thereby adjusting the temperatures of the first to fourth reactors so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressures of the four reactors are all 210 MPa. During the whole reaction process, the pulse control valve is intermittently opened, and the opening frequency is 80 s / time;

[0083] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. The temperature of the high-pressure separation tank is adjusted to 200 °C, and the pressure is 22 MPa;

[0084] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 180 °C, and the pressure is 40 kPa;

[0085] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0086] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at 25 °C for 36 h to obtain the EVA product.

[0087] That is, the differences between this comparative example and Example 1 are as follows: the temperature of high-pressure separation is 200 °C, the pressure of high-pressure separation is 22 MPa, the temperature of low-pressure separation is 180 °C, and the pressure of low-pressure separation is 40 kPa.

[0088] Comparative Example 4

[0089] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0090] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipe (the feed rate is 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into the secondary compressor through the compression pipeline;

[0091] Vinyl acetate (i.e., VA, the feed rate is 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa;

[0092] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (which consists of isododecane as the diluent, di-sec-butyl peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxy-2-ethylhexanoate in a mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the inlet of each reactor stage and is injected into the four reactors at four points (where the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction starts;

[0093] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the heat can be dissipated by adjusting the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, where the low-pressure hot water temperature is 120 °C and the medium-pressure hot water temperature is 125 °C), thereby adjusting the temperatures of the first to fourth reactors so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressures of the four reactors are all 210 MPa, and the pulse control valve is intermittently opened throughout the reaction, with an opening frequency of 80 s / time;

[0094] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. The temperature of the high-pressure separation tank is adjusted to 200 °C and the pressure is adjusted to 20 MPa;

[0095] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 200 °C and the pressure is adjusted to 10 kPa;

[0096] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0097] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at 30 °C for 36 h to obtain the EVA product.

[0098] That is, the differences between this comparative example and Example 1 are as follows: the temperature of high-pressure separation is 200 °C, the pressure of high-pressure separation is 20 MPa, the temperature of low-pressure separation is 200 °C, the pressure of low-pressure separation is 10 kPa, and the degassing temperature is 30 °C.

[0099] Comparative Example 5

[0100] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the examples in CN110563871A. The specific steps are as follows:

[0101] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipeline (the feed rate is 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into the secondary compressor through the compression pipeline;

[0102] Vinyl acetate (i.e., VA, the feed rate is 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa;

[0103] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (the initiator is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, and tert-butyl peroxy-2-ethylhexanoate according to the mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor and is injected into the four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction starts;

[0104] Since the polymerization reaction of ethylene and vinyl acetate is a strong exothermic reaction, the temperature of the first to fourth reactors can be adjusted by regulating the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, where the low-pressure hot water temperature is 120 °C and the medium-pressure hot water temperature is 125 °C) to dissipate heat, so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressure of the four reactors is 210 MPa, and the pulse control valve is intermittently opened throughout the reaction, and the opening frequency is 80 s / time;

[0105] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. Adjust the temperature of the high-pressure separation tank to 200 °C and the pressure to 21 MPa;

[0106] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. Adjust the temperature of the low-pressure separation tank to 198 °C and the pressure to 65 kPa;

[0107] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0108] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at a temperature of 21 °C for 36 h to obtain the EVA product.

[0109] That is, the differences between this comparative example and Example 1 are as follows: the temperature of high-pressure separation is 200 °C, the pressure of high-pressure separation is 21 MPa, the temperature of low-pressure separation is 198 °C, the pressure of low-pressure separation is 65 kPa, and the degassing temperature is 21 °C.

[0110] Comparative Example 6

[0111] A production method of ethylene-vinyl acetate copolymer resin, which is carried out in the production device of the example in CN110563871A. The specific steps are as follows:

[0112] S1. Compression: Ethylene gas enters the primary compressor through the ethylene feed pipeline (feed rate: 20 t / h). The primary compressor compresses the ethylene gas to 20 MPa. Subsequently, the compressed ethylene gas is sent into the secondary compressor through the compression pipeline;

[0113] Vinyl acetate (i.e., VA, feed rate: 11 t / h) enters the secondary compressor through the vinyl acetate feed pipeline. In the secondary compressor, vinyl acetate is mixed with the compressed ethylene gas to obtain a mixture, and the secondary compressor compresses the mixture to 220 MPa;

[0114] S2. Polymerization: The mixture compressed to 220 MPa enters the preheater through the connecting pipeline between the secondary compressor and the preheater. The preheater heats the mixture to the initiation temperature of the initiator. The initiator (which is composed of diluent isododecane, di-sec-butyl peroxydicarbonate, tert-butyl peroxyneoheptanoate, tert-butyl peroxyneopentanoate, and tert-butyl peroxy-2-ethylhexanoate in a mass percentage of 58 wt%: 20 wt%: 10 wt%: 6 wt%: 6 wt%) enters the production device through the initiator injection pipeline connected to the feed port of each stage of the reactor and is injected into the four reactors at four points (wherein, the injection amount of the initiator in the first-stage reactor is 41 kg / h; the injection amount of the initiator in the second-stage reactor is 37 kg / h; the injection amount of the initiator in the third-stage reactor is 32 kg / h; the injection amount of the initiator in the fourth-stage reactor is 27 kg / h). After the initiator is injected, the polymerization reaction starts;

[0115] Since the polymerization reaction of ethylene and vinyl acetate is a strongly exothermic reaction, the temperature of the first to fourth reactors can be adjusted by regulating the hot water system (equipped with a low-pressure hot water station and a medium-pressure hot water station, wherein the temperature of the low-pressure hot water is 120 °C and the temperature of the medium-pressure hot water is 125 °C) to dissipate heat, so that the reaction temperature in the first reactor is 200 °C, the reaction temperature in the second reactor is 200 °C, the reaction temperature in the third reactor is 210 °C, and the reaction temperature in the fourth reactor is 215 °C. The pressure of the four reactors is 210 MPa. The pulse control valve is intermittently opened throughout the reaction, and the opening frequency is 80 s / time;

[0116] S3. High-pressure separation: The melt generated after the reaction in step S2 enters the high-pressure separation tank through the connecting pipeline between the fourth-stage reactor and the high-pressure separation tank. The temperature of the high-pressure separation tank is adjusted to 200 °C and the pressure is 21 MPa;

[0117] S4. Low-pressure separation: The melt after high-pressure separation enters the low-pressure separation tank through the connecting pipeline between the high-pressure separation tank and the low-pressure separation tank. The temperature of the low-pressure separation tank is adjusted to 198 °C and the pressure is 45 kPa;

[0118] S5. Pelletizing: The melt after low-pressure separation enters the extruder, and the melt is extruded into pellets in the extruder to obtain EVA pellets;

[0119] S6. Degassing: Subsequently, the EVA pellets are sent to the degassing silo and degassed at a temperature of 21 °C for 36 h to obtain the EVA product.

[0120] That is, the differences between this comparative example and Example 1 are: the temperature of high-pressure separation is 200 °C, the pressure of high-pressure separation is 21 MPa, the temperature of low-pressure separation is 198 °C, the pressure of low-pressure separation is 45 kPa, and the degassing temperature is 21 °C.

[0121] Detection

[0122] The volatile content in the EVA products prepared in Examples 1-3 and Comparative Examples 1-6 was detected in accordance with "Plastics - Homopolymers and Copolymers of Vinyl Chloride - Determination of Volatile Matter (Including Water) - GB / T 2914-2008 / ISO 1269:2006". The results are shown in Table 1;

[0123] The material consumption and energy consumption in the process of producing EVA products according to the production methods of Examples 1-3, Comparative Examples 1-4 and Comparative Example 6 were calculated. The results are shown in Table 1;

[0124] Among them, the material consumption was calculated according to the formula: material consumption = (ethylene consumption + vinyl acetate consumption) / EVA product output;

[0125] The energy consumption was calculated according to the formula: energy consumption = Σ[(consumption of each fuel and power medium involved in the production of EVA products) / EVA product output * (standard coal conversion coefficient of each fuel and power medium)], where

[0126] The standard coal conversion coefficient of tap water, a fuel and power medium involved in the production of EVA products, is 0.17;

[0127] The standard coal conversion coefficient of production water, a fuel and power medium involved in the production of EVA products, is 0.17;

[0128] The standard coal conversion coefficient of demineralized water, a fuel and power medium involved in the production of EVA products, is 2.3;

[0129] The standard coal conversion coefficient of circulating water, a fuel and power medium involved in the production of EVA products, is 0.1;

[0130] The standard coal conversion coefficient of high-pressure steam (4.2 MPa), a fuel and power medium involved in the production of EVA products, is 88.0; the standard coal conversion coefficient of low-pressure steam (0.4 MPa), a fuel and power medium involved in the production of EVA products, is 66.0; the standard coal conversion coefficient of plant air, a fuel and power medium involved in the production of EVA products, is 0.028;

[0131] The standard coal conversion coefficient of instrument air, a fuel and power medium involved in the production of EVA products, is 0.038;

[0132] The standard coal conversion coefficient of nitrogen gas (0.7 MPa), a fuel and power medium involved in the production of EVA products, is 0.15;

[0133] The standard coal conversion coefficient of natural gas, a fuel and power medium involved in the production of EVA products, is 950.0;

[0134] The standard coal conversion coefficient of electricity, a fuel and power medium involved in the production of EVA products, is 220.0;

[0135] The standard coal conversion coefficient of condensate, a fuel and power medium involved in the production of EVA products, is 7.65.

[0136] Table 1 Test Results

[0137]

[0138] Note: / indicates not measured.

[0139] As can be seen from Table 1, compared with Comparative Examples 1-6, the volatile content in the ethylene-vinyl acetate copolymer resin prepared in Examples 1-3 is significantly reduced, and the material consumption and energy consumption are also reduced. This result shows that the method of the present invention can significantly reduce the volatile content in the prepared ethylene-vinyl acetate copolymer resin while reducing the material consumption and energy consumption.

[0140] As can be seen from Table 1, for Comparative Example 1 (the pressure of low-pressure separation is not within the range of 43-48 kPa, the temperature of low-pressure separation is not within the range of 183-187 °C, the pressure of high-pressure separation is not within the range of 20.5-21.5 MPa, and the temperature of high-pressure separation is not within the range of 183-187 °C), the material consumption is 1.025 t / t, the energy consumption is 278 kg standard oil / t, and the volatile content in the prepared ethylene-vinyl acetate copolymer resin is 0.32%; for Comparative Example 2 (the pressure of low-pressure separation is not within the range of 43-48 kPa, the temperature of low-pressure separation is not within the range of 183-187 °C, the pressure of high-pressure separation is not within the range of 20.5-21.5 MPa, the temperature of high-pressure separation is not within the range of 183-187 °C, and the degassing temperature is not within the range of 22-25 °C), the material consumption is 1.022 t / t, the energy consumption is 272 kg standard oil / t, and the volatile content in the prepared ethylene-vinyl acetate copolymer resin is 0.29%; while for Examples 1-3 (the pressure of low-pressure separation is within the range of 43-48 kPa, the temperature of low-pressure separation is within the range of 183-187 °C, the pressure of high-pressure separation is within the range of 20.5-21.5 MPa, the temperature of high-pressure separation is within the range of 183-187 °C, and the degassing temperature is within the range of 22-25 °C), the material consumption is 1.016-1.017 t / t, the energy consumption is 267-269 kg standard oil / t, and the volatile content in the prepared ethylene-vinyl acetate copolymer resin is 0.14%-0.16%. This result shows that by optimizing the pressure and temperature of low-pressure separation, the pressure and temperature of high-pressure separation, and the degassing temperature in the present application, the volatile content in the prepared ethylene-vinyl acetate copolymer resin can be significantly reduced while reducing the material consumption and energy consumption.

[0141] As can be seen from Table 1, the volatile content in the ethylene-vinyl acetate copolymer resin prepared in Comparative Example 5 (where the pressure of low-pressure separation is not within the range of 43-48 kPa) is 0.26%, while the volatile content in the ethylene-vinyl acetate copolymer resin prepared in Comparative Example 6 (where the pressure of low-pressure separation is within the range of 43-48 kPa, specifically 45 kPa) is 0.16%. This result shows that controlling the pressure of low-pressure separation within the range of 43-48 kPa can significantly reduce the volatile content in the prepared ethylene-vinyl acetate copolymer resin.

[0142] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A production method of ethylene-vinyl acetate copolymer, which uses ethylene and vinyl acetate as raw materials and successively includes compression, polymerization, high-pressure separation, low-pressure separation, granulation and degassing processes, characterized in that, The temperature of the polymerization is 200 - 250 °C, and the pressure of the polymerization is 200 - 250 MPa; during the high-pressure separation process, the pressure is 20.5 - 21.5 MPa and the temperature is 183 - 190 °C; during the low-pressure separation process, the pressure is 43 - 48 kPa and the temperature is 183 - 187 °C; the temperature of the degassing is 22 - 25 °C, and the duration of the degassing is 35 - 37 h.

2. The production method according to claim 1, characterized in that, Compressed to 20 - 260 MPa.

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