Olefin gas phase copolymerization system and method

Abstract

The invention belongs to the technical field of olefin gas phase polymerization, and discloses an olefin gas phase copolymerization system and method.The system comprises a polymerization kettle, a gas distribution tank and a circulating compressor, a gas inlet of the polymerization kettle is connected with a gas outlet of the gas distribution tank through a gas inlet pipeline, and a gas outlet of the polymerization kettle is connected with the gas distribution tank through a circulating gas pipeline; and the circulating compressor is arranged on the gas inlet pipeline or the circulating gas pipeline. The olefin gas phase copolymerization system and the olefin gas phase copolymerization method can reduce fluctuation of gas composition in the polymerization kettle and maintain the effect that the gas composition in the polymerization kettle is basically stable, so that a polymer product with stable and controllable composition is obtained, and the olefin gas phase copolymerization system and the olefin gas phase copolymerization method have the characteristics of less equipment, simple process and easiness in operation.

Description

Technical Field

[0001] The invention belongs to the technical field of olefin gas phase polymerization, and in particular, relates to an olefin gas phase copolymerization system and method. Background Art

[0002] Olefin gas phase copolymerization is an important part of polyolefin process and is widely used in the production process of linear low density polyethylene, random copolymer polypropylene and impact copolymer polypropylene. In the process of olefin gas phase copolymerization, the ratio of various olefins in the gas phase in the reactor is different, and the properties of the copolymer obtained by polymerization are also very different. Therefore, the relationship between process gas composition and copolymer performance is one of the important research contents of olefin gas phase copolymerization.

[0003] Polyolefin industrial plants and pilot plants can achieve stable gas composition during polymerization through complex feed system control, but they also have disadvantages such as high research cost and inflexible switching of conditions. Olefin gas phase copolymerization research on small-scale pilot plants can avoid the above disadvantages.

[0004] Bergstra et al. (Chemical Engineering Science, 2006, 61: 4909-4918) provided a small-scale test device for olefin gas phase copolymerization research. The device refers to industrial and pilot plants. By installing flow control instruments on each raw material feed pipeline of the polymerization reactor and combining an instrument for online analysis of gas phase composition, the purpose of stabilizing the gas phase composition during olefin copolymerization is achieved. However, the device also has the disadvantages of high investment and complex control.

[0005] Cancelas et al. (Macromolecular Reaction Engineering, 2018, 12, 1700063) studied the relationship between the polymerization conditions of impact polypropylene and the properties of the polymer. It provides another method for studying the gas phase copolymerization of olefins, which requires the prior knowledge of the corresponding relationship between the gas composition of the olefin copolymerization and the polymer composition, and assumes that the reactivity ratio between monomers does not change during the polymerization process. The specific steps are to prepare a gas phase monomer mixture with the same composition ratio as the target product in the gas distribution tank; at the beginning of the olefin copolymerization, first establish the gas phase composition of the polymerization kettle according to the polymerization monomer ratio required by the target product composition ratio, and then switch the polymerization kettle air intake to the gas distribution tank gas, in order to obtain a stable gas phase composition in the polymerization kettle. This method reduces equipment investment and is simple to operate, but for new catalyst systems, it is difficult to control the stable gas phase composition during the copolymerization process when the relationship between the copolymerization olefin monomer composition and the polymer composition is unknown. Summary of the invention

[0006] For the copolymerization reaction of olefins, the different consumption rates of different olefin monomers in the polymerization kettle caused by the difference in the reactivity ratio of different olefin monomers bring difficulties to the stable control of the gas composition during the olefin copolymerization process. In view of the problems existing in the prior art, the purpose of the present invention is to provide a system and method for gas phase copolymerization of olefins. The system and method of the present invention can achieve a stable gas composition in the polymerization kettle, thereby obtaining a polymer product with controllable composition.

[0007] The first aspect of the present invention provides an olefin gas phase copolymerization system, which includes a polymerization kettle, a gas distribution tank and a circulating compressor, wherein the air inlet of the polymerization kettle is connected to the air outlet of the gas distribution tank via an air inlet pipeline, the air outlet of the polymerization kettle is connected to the gas distribution tank via a circulating gas pipeline, and the circulating compressor is arranged on the air inlet pipeline or the circulating gas pipeline.

[0008] The second aspect of the present invention provides a method for gas phase copolymerization of olefins using the above system, the method comprising:

[0009] 1) preparing a mixed gas containing copolymerized olefins in a gas distribution tank, wherein the total amount of olefins in the mixed gas is A mol;

[0010] 2) Olefin gas phase copolymerization stage: the gas distribution tank is connected to the polymerization kettle, the copolymerization olefin gas is introduced into the polymerization kettle, and the gas is circulated between the polymerization kettle and the gas distribution tank through a circulation compressor, and the polymerization kettle performs copolymerization reaction;

[0011] 3) After the copolymerization reaction is completed, the gas circulation is stopped and the unreacted monomers in the polymerization kettle are recovered. The total amount of olefins consumed in the copolymerization is B mol, and A / B is greater than 4.

[0012] The present invention can reduce the fluctuation of gas composition in the polymerization kettle by adding a circulating compressor between the polymerization kettle and the gas distribution tank to make the gas between the polymerization kettle and the gas distribution tank circulate during the copolymerization process. Furthermore, by selecting a suitable gas distribution amount and circulating gas speed, the effect of maintaining the gas composition in the polymerization kettle is basically stable, thereby obtaining a polymer product with stable composition and controllable. Compared with most existing olefin gas phase copolymerization processes, the system and method of olefin gas phase copolymerization of the present invention have the characteristics of less equipment, simple process and easy operation, and realize the stability of gas composition in the reactor during the copolymerization process, and can be used for the research and development of most existing olefin copolymerization processes and product technologies.

[0013] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a structural schematic diagram of an olefin gas phase copolymerization system.

[0015] Figure 2 This is a schematic diagram of the structure of another olefin gas phase copolymerization system.

[0016] Explanation of the reference numerals: 1-polymerization kettle; 2-gas distribution tank; 3-circulation compressor; 4-pressure reducing valve; 5-back pressure valve. DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0018] According to a first aspect of the present invention, the present invention provides an olefin gas phase copolymerization system, which includes a polymerization kettle, a gas distribution tank and a circulating compressor, wherein the air inlet of the polymerization kettle is connected to the air outlet of the gas distribution tank via an air inlet pipeline, the air outlet of the polymerization kettle is connected to the gas distribution tank via a circulating gas pipeline, and the circulating compressor is arranged on the air inlet pipeline or the circulating gas pipeline.

[0019] According to the present invention, the polymerization kettle provides a place for olefin copolymerization, which can be a pressure-resistant reaction vessel conventionally used in the art, with a maximum pressure of 4.0 to 10.0 MPa, a maximum temperature of 100 to 300° C., and is equipped with a stirrer and a temperature control system; a volume of 0.001 to 10 m 3 .

[0020] In the present invention, the gas distribution tank provides reaction gas for olefin copolymerization, which is a pressure-resistant container with a maximum pressure of 1.0 to 10.0 MPa and a maximum temperature of 100 to 300° C., preferably equipped with a heating system; a volume of 0.01 to 1000 m 3 .

[0021] According to the present invention, the volume ratio of the gas distribution tank to the polymerization kettle is not less than 5, preferably not less than 15, and more preferably not less than 20.

[0022] In the present invention, the circulating compressor is used to realize the gas circulation between the polymerization kettle and the gas distribution tank. The circulating compressor can select a conventional model, which generally needs to meet the inlet pressure of 0.1-10MPa, the outlet pressure is higher than the inlet pressure of 0-1.0MPa, and the circulating gas speed is not less than 1NL / min.

[0023] According to one embodiment, the pressure of the polymerization kettle is greater than the pressure of the gas distribution tank, the circulating compressor is arranged on the air inlet pipeline, the circulating gas pipeline is provided with a first pressure control unit, the first pressure control unit is a first regulating valve or a back pressure valve (such as a self-operated back pressure valve), the first regulating valve is electrically connected to the pressure instrument signal of the polymerization kettle, and the signal connection enables the opening size of the first regulating valve and the pressure setting value of the polymerization kettle to be automatically controlled, which is a more conventional automatic control and can be achieved by referring to the prior art. This combination can provide a higher pressure selection range in the polymerization kettle during copolymerization, which is conducive to improving the yield of copolymerization.

[0024] According to another embodiment, the pressure of the polymerization kettle is lower than the pressure of the gas distribution tank, the circulating compressor is arranged on the circulating gas pipeline, the air intake pipeline is provided with a second pressure control unit, the second pressure control unit is a second regulating valve or a pressure reducing valve (such as a self-operated pressure reducing valve), the second regulating valve is electrically connected to the pressure instrument signal of the polymerization kettle, and the signal connection enables automatic control of the opening size of the second regulating valve and the pressure setting value of the polymerization kettle.

[0025] According to a second aspect of the present invention, the present invention provides a method for gas phase copolymerization of olefins using the above system, the method comprising:

[0026] 1) preparing a mixed gas containing copolymerized olefins in a gas distribution tank, wherein the total amount of olefins in the mixed gas is A mol;

[0027] 2) Olefin gas phase copolymerization stage: the gas distribution tank is connected to the polymerization kettle, the copolymerization olefin gas is introduced into the polymerization kettle, and the gas is circulated between the polymerization kettle and the gas distribution tank through a circulation compressor, and the polymerization kettle performs copolymerization reaction;

[0028] 3) After the copolymerization reaction is completed, stop the gas circulation (stop the circulation compressor, close the valve on the gas pipeline between the polymerization kettle and the gas distribution tank), recover the unreacted monomers in the polymerization kettle, and the total amount of olefins consumed in the copolymerization is B mol, and A / B is greater than 4.

[0029] In the present invention, the total amount A of olefins in the mixed gas prepared in the gas distribution tank is determined by the yield of copolymerization, that is, the total amount B of olefins finally consumed in the copolymerization. Preferably, A / B is greater than 5, and more preferably A / B is greater than 10.

[0030] According to the present invention, the mixed gas in step 1) contains at least copolymerized olefins according to different target products, and the copolymerized olefins can be selected from at least two of ethylene, propylene, and α-olefins containing 4 to 10 carbon atoms; the mixed gas can also contain one or more of hydrogen, alkanes and inert gases.

[0031] The total pressure of the mixed gas is 0.1-10MPa. The prepared mixed gas must meet the requirement that all gas components cannot be liquefied under the final gas distribution tank pressure, that is, the lowest temperature inside the gas distribution tank must be higher than the dew point of all gas components under the partial pressure of the components. The total amount of olefins in the prepared gas A can be calculated by measuring the various olefin feed amounts separately, or it can be estimated by sampling the prepared gas and analyzing it by chromatography according to the standard gas equation.

[0032] The olefin gas phase copolymerization method of the present invention is suitable for the study of single olefin gas phase copolymerization, such as the copolymerization of ethylene and a small amount of propylene, or ethylene and a small amount of alpha olefin with carbon number of 4 to 10, or the copolymerization of propylene and a small amount of ethylene, propylene and a small amount of alpha olefin with carbon number of 4 to 10, or propylene and two or more selected from ethylene and alpha olefin with carbon number of 4 to 10; it is also suitable for the olefin gas phase copolymerization stage of multi-stage polymerization, that is, a homopolymerization stage is provided before the olefin gas phase copolymerization stage, such as the copolymerization stage of propylene homopolymerization + ethylene-propylene copolymerization, etc.

[0033] When a single olefin gas phase copolymerization is carried out, or when the olefin gas phase copolymerization is in the first stage of a multi-stage polymerization process, in order to prevent the melting and agglomeration of the polymer particles after the start of the polymerization, it is necessary to add inert particles into the polymerization kettle in advance as a dispersant for the catalyst particles; when the olefin gas phase copolymerization is in the second stage or other subsequent stages of a multi-stage polymerization, there is no need to add inert particles separately.

[0034] In the present invention, the specific parameters of the gas phase copolymerization stage can be conventionally selected according to the prior art, for example, the copolymerization temperature is 10 to 100° C., the copolymerization pressure is 0.1 to 10 MPa, and the copolymerization time is 1 to 10000 min.

[0035] Components, components and parameters not limited in the present invention may be selected according to the prior art and belong to conventional technical means in the field.

[0036] The present invention will be further described below with reference to the following examples, but is not limited to these examples.

[0037] Example 1

[0038] Process flow such as Figure 1 The polymerization kettle 1 is a 5.0-liter stirred stainless steel kettle with a jacket of hot water for temperature control; the gas distribution tank 2 is an 80-liter stainless steel storage tank with a jacket of hot water for temperature control; the circulating compressor 3 is an air-driven piston gas booster with a flow rate of 63NL / min.

[0039] Gas distribution: Turn on the hot water in the jacket of the gas distribution tank, control the temperature inside the tank at 60-70°C, and flush propylene, ethylene and hydrogen into the gas distribution tank at a partial pressure ratio of 10:4:0.5. The final gauge pressure of the gas distribution tank is 1.35MPa.

[0040] Liquid phase homopolymerization of propylene: At room temperature, 14.8 mg of DQ catalyst, 1.5 mmol of triethylaluminum, 0.2 mmol of methylcyclohexyldimethoxysilane were added to the polymerization kettle, and then 0.1 g of hydrogen was added; stirring was started, and 2.0 liters of liquid propylene was added to the polymerization kettle through the metering tank, and then the polymerization kettle temperature control system was started to quickly raise the kettle temperature to 70°C, and the propylene liquid phase bulk homopolymerization was carried out for 0.5 hours.

[0041] Propylene and ethylene gas phase copolymerization: After the homopolymerization of propylene is completed, the unreacted monomers are vented, the valve on the gas distribution tank to the polymerization kettle pipeline is opened, and the mixed gas is introduced into the kettle. The reactor temperature is set to 70°C; then the valve from the outlet of the polymerization kettle to the circulating compressor is opened, the circulating compressor is started, and finally the valve from the outlet of the circulating compressor to the gas distribution tank is opened. The pressure reducing valve 4 on the gas distribution tank to the polymerization kettle inlet pipeline is adjusted to stabilize the kettle pressure at 0.8MPa, and then the gas sample R-1 is taken from the polymerization kettle, and the gas sample R-2 is taken after 60 minutes, and then the circulating compressor is stopped, the valves on the polymerization kettle inlet pipeline and outlet pipeline are closed, and the unreacted monomers in the kettle are vented and the material is discharged to obtain 375 grams of impact copolymerized polypropylene. The polymer was analyzed and tested, and the ethylene mass content was 7.51% and the rubber phase mass content was 18.04%. The relevant experimental results are shown in Table 1.

[0042] Example 2

[0043] Process flow such as Figure 1 As shown, the polymerization kettle is 3.4 liters, the gas distribution tank is 20 liters, propylene, ethylene and hydrogen are injected into the gas distribution tank according to the partial pressure ratio of 10:3:0.5, and the final gas distribution tank gauge pressure is 1.25MPa. Other polymerization conditions are the same as those in Example 1, and finally 323 grams of impact copolymerized polypropylene is obtained. The polymer is analyzed and tested, and the ethylene mass content is 4.58% and the rubber phase mass content is 11.14%. The relevant experimental results are shown in Table 1.

[0044] Example 3

[0045] Process flow such as Figure 2 As shown, the polymerization kettle is 5.0 liters, the gas distribution tank is 118 liters, propylene and ethylene are injected into the gas distribution tank according to the partial pressure ratio of 7:3, the gas distribution pressure is 0.9 MPa, the propylene homopolymerization time is 60 minutes, the ethylene-propylene copolymerization time is 60 minutes, the copolymerization pressure is 1.4 MPa, and the other polymerization conditions are the same as those in Example 1. Finally, 363 grams of impact copolymerized polypropylene is obtained. The polymer is analyzed and tested, and the ethylene mass content is 12.44% and the rubber phase mass content is 27.57%. The relevant experimental results are shown in Table 1.

[0046] Example 4

[0047] Process flow such as Figure 2As shown, the polymerization kettle is 5.0 liters, the gas distribution tank is 118 liters, propylene and ethylene are injected into the gas distribution tank according to the partial pressure ratio of 4:2, the gas distribution pressure is 0.6MPa, the catalyst is BCM catalyst, the external electron donor is diisopropyldimethoxysilane, the propylene homopolymerization time is 30 minutes, the ethylene-propylene copolymerization time is 60 minutes, and the other polymerization conditions are the same as those in Example 3. Finally, 700 grams of impact copolymerized polypropylene is obtained. The polymer is analyzed and tested, and the ethylene mass content is 10.12% and the rubber phase mass content is 28.96%. The relevant experimental results are shown in Table 1.

[0048] Example 5

[0049] Process flow such as Figure 2 As shown, the polymerization kettle is 5.0 liters, the gas distribution tank is 118 liters, propylene and ethylene are injected into the gas distribution tank at a partial pressure ratio of 4:1, the gas distribution pressure is 0.55MPa, the catalyst is BCM catalyst, the external electron donor is diisopropyldimethoxysilane, the propylene homopolymerization time is 30 minutes, the ethylene-propylene copolymerization time is 120 minutes, and the other polymerization conditions are the same as those in Example 3. Finally, 632 grams of impact copolymerized polypropylene are obtained. The polymer is analyzed and tested, and the ethylene mass content is 13.63% and the rubber phase mass content is 38.07%. The relevant experimental results are shown in Table 1.

[0050] Comparative Example 1

[0051] Except that the circulating compressor was not started and the gas outlet of the polymerization kettle was closed, other polymerization conditions were the same as those in Example 1, and 267 grams of impact copolymer polypropylene was finally obtained. The polymer was analyzed and tested, and the ethylene mass content was 9.50%, and the rubber phase mass content was 24.35%. The relevant experimental results are shown in Table 1.

[0052] Comparative Example 2

[0053] Except that the circulating compressor was not started and the gas outlet of the polymerization kettle was closed, other polymerization conditions were the same as those in Example 2, and 394 grams of impact copolymer polypropylene was finally obtained. The polymer was analyzed and tested, and the ethylene mass content was 4.11%, and the rubber phase mass content was 11.27%. The relevant experimental results are shown in Table 1.

[0054] Table 1

[0055]

[0056] Note: “E / P” is the volume ratio of ethylene to propylene obtained by chromatographic analysis of gas samples.

[0057] As shown in Table 1, the system and method for gas phase copolymerization of olefins of the present invention can make the E / P fluctuation range lower than 15%, can effectively control the gas composition in the polymerization kettle during the copolymerization process, thereby producing a copolymer product with stable composition, and when the gas distribution amount / polymerization amount (A / B, mol / mol) is greater than 5.0 and the volume ratio of the gas distribution tank to the polymerization kettle is greater than 5.0, the fluctuation range of the gas phase composition in the polymerization kettle at the start and end of the copolymerization process can be less than 10%; in a more preferred case (such as Examples 1 and 3), when the gas distribution amount / polymerization amount (A / B, mol / mol) is greater than 15 and the volume ratio of the gas distribution tank to the polymerization kettle is greater than 15, the fluctuation range of the gas phase composition in the polymerization kettle at the start and end of the copolymerization process is less than 5%. On the contrary, it can be seen from the comparative example that when there is no gas circulation between the gas distribution tank and the polymerization kettle during the copolymerization process, the fluctuation range of the gas phase composition in the polymerization kettle at the start and end of the copolymerization exceeds 40%, and the structural composition of the copolymer obtained by polymerization in this case is very inhomogeneous, and the product quality and stability will also be greatly affected.

[0058] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An olefin gas phase copolymerization system, characterized in that: The system comprises a polymerization kettle, a gas distribution tank and a circulation compressor. The air inlet of the polymerization kettle is connected to the air outlet of the gas distribution tank through an air inlet pipeline, the air outlet of the polymerization kettle is connected to the gas distribution tank through a circulation gas pipeline, and the circulation compressor is arranged on the air inlet pipeline or the circulation gas pipeline.

2. The olefin gas phase copolymerization system according to claim 1, wherein: The volume ratio of the gas distribution tank to the polymerization kettle is not less than 5.

3. The olefin gas phase copolymerization system according to claim 2, wherein: The volume ratio of the gas distribution tank to the polymerization kettle is not less than 15, preferably not less than 20.

4. The olefin gas phase copolymerization system according to claim 1, wherein: The circulating compressor is arranged on the air inlet pipeline, and a first pressure control unit is arranged on the circulating air pipeline. The first pressure control unit is a first regulating valve or a back pressure valve, and the first regulating valve is electrically connected to the pressure instrument signal of the polymerization kettle.

5. The olefin gas phase copolymerization system according to claim 1, wherein: The circulating compressor is arranged on the circulating gas pipeline, and the air intake pipeline is provided with a second pressure control unit, which is a second regulating valve or a pressure reducing valve, and the second regulating valve is electrically connected to the pressure instrument signal of the polymerization kettle.

6. A method for gas phase copolymerization of olefins using the system according to any one of claims 1 to 5, characterized in that: The method includes: 1) preparing a mixed gas containing copolymerized olefins in a gas distribution tank, wherein the total amount of olefins in the mixed gas is A mol; 2) Olefin gas phase copolymerization stage: the gas distribution tank is connected to the polymerization kettle, the copolymerization olefin gas is introduced into the polymerization kettle, and the gas is circulated between the polymerization kettle and the gas distribution tank through a circulation compressor, and the polymerization kettle performs copolymerization reaction; 3) After the copolymerization reaction is completed, the gas circulation is stopped and the unreacted monomers in the polymerization kettle are recovered. The total amount of olefins consumed in the copolymerization is B mol, and A / B is greater than 4.

7. The olefin gas phase copolymerization method according to claim 6, wherein: A / B is greater than 5, preferably A / B is greater than 10.

8. The method for gas phase copolymerization of olefins according to claim 6, wherein The copolymerized olefins are selected from at least two of ethylene, propylene and α-olefins containing 4 to 10 carbon atoms.

9. The method for gas phase copolymerization of olefins according to claim 6, wherein: The mixed gas also contains one or more of hydrogen, alkane and inert gas.

10. The olefin gas phase copolymerization method according to claim 6, wherein: The conditions of the copolymerization reaction include: a copolymerization temperature of 10 to 100° C., a copolymerization pressure of 0.1 to 10 MPa, and a copolymerization time of 1 to 10000 min.

11. The olefin gas phase copolymerization method according to claim 6, wherein: The olefin gas phase copolymerization stage is preceded by a homopolymerization stage.

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