Olefin gas-phase copolymerization system and method

Abstract

The present application belongs to the technical field of olefin gas phase polymerization, and discloses an olefin gas phase copolymerization system and method, which comprises a polymerization kettle, a gas distribution tank and a circulating compressor, the gas inlet of the polymerization kettle is connected with the gas outlet of the gas distribution tank through a gas inlet pipeline, the 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 method can reduce the fluctuation of the gas composition in the polymerization kettle, maintain the effect of keeping the gas composition in the polymerization kettle basically stable, thereby obtaining polymer products with stable and controllable composition, and have the characteristics of less equipment, simple process and easy operation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of olefin gas phase polymerization, and particularly relates to an olefin gas phase copolymerization system and method. BACKGROUND

[0002] Olefin gas phase copolymerization is an important part of polyolefin process, which is widely used in the production process of linear low density polyethylene, random copolymer polypropylene and impact copolymer polypropylene products. In the process of olefin gas phase copolymerization, the proportion of various olefins in the gas phase in the reactor is different, and the properties of the copolymer obtained by polymerization are also greatly different, so the study of the relationship between the process gas composition and the 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 in the polymerization process through complex feed system control, but at the same time there are disadvantages such as high research cost and inflexible condition switching. The research on olefin gas phase copolymerization on a small test device can avoid the above shortcomings.

[0004] Bergstra et al. (Chemical Engineering Science, 2006, 61: 4909-4918) provides a small test device for olefin gas phase copolymerization research. The device refers to industrial and pilot plants, and by installing flow control instruments on the raw material feeding pipelines of the polymerization kettle, combined with online analysis gas composition instruments, the purpose of stable gas composition in the process of olefin copolymerization is achieved. However, this 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. Among them, another method for researching olefin gas phase copolymerization is provided, which needs to know the corresponding relationship between the gas composition of olefin copolymerization and the composition of the polymer in advance, and assumes that the monomer reactivity does not change in the polymerization process. The specific steps are as follows: prepare a gas phase monomer mixture with the same composition ratio as the target product in a gas preparation 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 gas inlet of the polymerization kettle to the gas of the gas preparation tank, so as to obtain stable gas composition in the polymerization kettle. This method reduces the equipment investment and is simple to operate, but for new catalyst systems, it is difficult to control the stable gas composition in the copolymerization process when the relationship between the copolymerization olefin monomer composition and the polymer composition is unknown. SUMMARY

[0006] For the copolymerization of olefins, the difference in the consumption rate of different olefin monomers in the polymerization reactor caused by the difference in the reactivity ratio of different olefin monomers brings difficulties to the stable control of the gas composition in the process of olefin copolymerization. In view of the problems existing in the prior art, the purpose of the present application is to provide an olefin gas phase copolymerization system and method, which can realize stable gas composition in the polymerization reactor and obtain polymer products with controllable composition by using the system and method of the present application.

[0007] The first aspect of the present application provides an olefin gas phase copolymerization system, which comprises a polymerization reactor, a gas distribution tank and a circulating compressor, the gas inlet of the polymerization reactor is connected with the gas outlet of the gas distribution tank through a gas inlet pipeline, the gas outlet of the polymerization reactor 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.

[0008] The second aspect of the present application provides an olefin gas phase copolymerization method using the above-mentioned system, which comprises:

[0009] 1) preparing a mixed gas containing copolymerization olefins in the gas distribution tank, the total amount of substances of the olefins in the mixed gas is Amol;

[0010] 2) olefin gas phase copolymerization stage: connecting the gas distribution tank with the polymerization reactor, introducing the copolymerization olefin gas into the polymerization reactor, and circulating the gas between the polymerization reactor and the gas distribution tank through the circulating compressor, and the polymerization reactor performs copolymerization reaction;

[0011] 3) after the copolymerization reaction is completed, stopping the gas circulation, recovering the unreacted monomers in the polymerization reactor, and the total amount of substances of the copolymerization consumed olefins is Bmol, and A / B is greater than 4.

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

[0013] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0016] BRIEF DESCRIPTION OF DRAWINGS 1 - polymerizer; 2 - gas distributor; 3 - circulating compressor; 4 - pressure reducing valve; 5 - back pressure valve. DETAILED DESCRIPTION

[0017] The specific embodiments of the present application are described in detail below. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, and are not by way of limitation.

[0018] According to the first aspect of the present application, the present application provides an olefin gas-phase copolymerization system, which comprises a polymerizer, a gas distributor and a circulating compressor, the gas inlet of the polymerizer is connected to the gas outlet of the gas distributor through a gas inlet pipeline, the gas outlet of the polymerizer is connected to the gas distributor through a circulating gas pipeline, and the circulating compressor is arranged on the gas inlet pipeline or the circulating gas pipeline.

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

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

[0021] According to the present application, the volume ratio of the gas distributor to the polymerizer is not less than 5, preferably not less than 15, and more preferably not less than 20.

[0022] In the present application, the circulating compressor is used to realize gas circulation between the polymerizer and the gas distributor, and the circulating compressor can be selected from conventional models, which generally need to meet the conditions of an inlet pressure of 0.1-10 MPa, an outlet pressure higher than the inlet pressure by 0-1.0 MPa, and a circulating gas velocity not less than 1 NL / min.

[0023] According to one embodiment, the pressure of the polymerization kettle is greater than the pressure of the gas tank, the circulating compressor is arranged on the gas inlet pipeline, a first pressure control unit is arranged on the circulating gas pipeline, 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 with the pressure instrument signal of the polymerization kettle, and the signal connection enables the opening degree of the first regulating valve to be automatically controlled according to the pressure set value of the polymerization kettle, which is a relatively conventional automatic control and can be realized by referring to the prior art. The combination can provide a higher pressure selection range in the polymerization kettle during copolymerization, and is beneficial to improving the yield of copolymerization.

[0024] According to another embodiment, the pressure of the polymerization kettle is less than the pressure of the gas tank, the circulating compressor is arranged on the circulating gas pipeline, and a second pressure control unit is arranged on the gas inlet pipeline, the second pressure control unit is a second regulating valve or a pressure reducing valve (such as a self-operated pressure reducing valve), and the second regulating valve is electrically connected with the pressure instrument signal of the polymerization kettle, and the signal connection enables the opening degree of the second regulating valve to be automatically controlled according to the pressure set value of the polymerization kettle.

[0025] According to a second aspect of the present application, the present application provides an olefin gas phase copolymerization method using the above-mentioned system, which comprises the following steps:

[0026] 1) preparing a mixed gas containing copolymerization olefins in the gas tank, the total amount of substances of the olefins in the mixed gas being Amol;

[0027] 2) olefin gas phase copolymerization stage: connecting the gas tank with the polymerization kettle, introducing the copolymerization olefin gas into the polymerization kettle, and circulating the gas between the polymerization kettle and the gas tank through the circulating compressor, so that the polymerization kettle performs copolymerization reaction;

[0028] 3) after the copolymerization reaction is completed, stopping the gas circulation (stopping the circulating compressor and closing the valve on the gas pipeline between the polymerization kettle and the gas tank), and recovering the unreacted monomers in the polymerization kettle, the total amount of substances of the copolymerization consumed olefins being Bmol, and A / B being greater than 4.

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

[0030] According to the present application, the mixed gas in step 1) contains at least copolymerization olefins according to different target products, and the copolymerization olefins can be selected from at least two of ethylene, propylene and α-olefins containing 4-10 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 0.1-10 MPa, and the prepared mixed gas should satisfy that no liquefaction phenomenon occurs to all gas components under the pressure of the final gas preparation tank, i.e. the lowest temperature point in the gas preparation tank is higher than the dew point of all gas components under the partial pressure of the components. The total amount of substance A of the olefins in the prepared gas can be calculated by separately metering various olefin feed amounts, or can be estimated by sampling and chromatographic analysis of the prepared gas according to the standard gas equation.

[0032] The olefin gas phase copolymerization method of the present application is suitable for individual olefin gas phase copolymerization research, such as copolymerization of ethylene with a small amount of propylene, or ethylene with a small amount of alpha olefin with carbon atom number of 4-10, or copolymerization of propylene with a small amount of ethylene, propylene with a small amount of alpha olefin with carbon atom number of 4-10, or propylene with two or more selected from ethylene and alpha olefin with carbon atom number of 4-10; and is also suitable for olefin gas phase copolymerization stage of multi-stage polymerization, i.e. a homopolymerization stage is provided before the olefin gas phase copolymerization stage, such as copolymerization stage of propylene homopolymerization + ethylene-propylene copolymerization, etc.

[0033] When individual olefin gas phase copolymerization is carried out, or the olefin gas phase copolymerization is located at the first stage of multi-stage polymerization, in order to prevent the melting and caking of polymer particles after the start of polymerization, it is necessary to add inert particles into the polymerization kettle in advance as a dispersant for catalyst particles; when the olefin gas phase copolymerization is located at the second stage or other stages of multi-stage polymerization, it is not necessary to separately add inert particles.

[0034] In the present application, the specific parameter conditions of the gas phase copolymerization stage can be selected according to the prior art. For example, the copolymerization temperature is 10-100℃, the copolymerization pressure is 0.1-10 MPa, and the copolymerization time is 1-10000 min.

[0035] In the present application, the components, components and parameters not limited can be selected according to the prior art, which belong to the conventional technical means in the art.

[0036] The present application will be further described below in conjunction with examples, but is not limited by these examples.

[0037] Example 1

[0038] The process flow is shown in Figure 1 The polymerization kettle 1 is a 5.0 liter stirring stainless steel kettle with jacketed hot water for temperature control; the gas preparation tank 2 is an 80 liter stainless steel storage tank with jacketed hot water for temperature control; the circulating compressor 3 is an air-driven piston type gas booster with a flow rate of 63 NL / min.

[0039] Gas preparation: open the jacketed hot water of the gas preparation tank, control the temperature in the tank at 60-70℃, and flush propylene, ethylene and hydrogen into the gas preparation tank according to the partial pressure ratio of 10:4:0.5, and the final gas preparation tank gauge pressure is 1.35 MPa.

[0040] Propylene liquid phase homopolymerization: 14.8 mg of DQ catalyst, 1.5 mmol of triethylaluminum, 0.2 mmol of methylcyclohexyldimethoxysilane were added into the polymerization reactor at room temperature, then 0.1 g of hydrogen was added; the stirring was started, 2.0 L of liquid propylene was added into the polymerization reactor through a metering tank, then the temperature control system of the polymerization reactor was started to rapidly increase the temperature of the reactor to 70°C, and the propylene liquid phase bulk polymerization was carried out for 0.5 h.

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

[0042] Example 2

[0043] The process flow is shown in Figure 1 The polymerization reactor was 3.4 L, the gas tank was 20 L, propylene, ethylene and hydrogen were introduced into the gas tank according to the partial pressure ratio of 10:3:0.5, and the final pressure of the gas tank was 1.25 MPa. The other polymerization conditions were the same as in Example 1, and finally 323 g of impact copolymer polypropylene was obtained. The polymer was analyzed and tested, the mass content of ethylene was 4.58%, and the mass content of the rubber phase was 11.14%. The related experimental results are shown in Table 1.

[0044] Example 3

[0045] The process flow is shown in Figure 2 The polymerization reactor was 5.0 L, the gas tank was 118 L, propylene and ethylene were introduced into the gas tank according to the partial pressure ratio of 7:3, the gas tank pressure was 0.9 MPa, the propylene homopolymerization time was 60 min, the ethylene-propylene copolymerization time was 60 min, the copolymerization pressure was 1.4 MPa, and the other polymerization conditions were the same as in Example 1. Finally, 363 g of impact copolymer polypropylene was obtained. The polymer was analyzed and tested, the mass content of ethylene was 12.44%, and the mass content of the rubber phase was 27.57%. The related experimental results are shown in Table 1.

[0046] Example 4

[0047] The process flow is shown in Figure 2The polymerization kettle is 5.0 liters, the gas tank is 118 liters, propylene and ethylene are injected into the gas tank according to a 4:2 partial pressure ratio, the gas tank pressure is 0.6 MPa, the catalyst is BCM catalyst, the external electron donor is diisopropyl dimethoxysilane, the propylene homopolymerization time is 30 minutes, the ethylene-propylene copolymerization time is 60 minutes, and other polymerization conditions are the same as in Example 3. Finally, 700 grams of impact copolymer 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] The process flow is shown in Figure 2 The polymerization kettle is 5.0 liters, the gas tank is 118 liters, propylene and ethylene are injected into the gas tank according to a 4:1 partial pressure ratio, the gas tank pressure is 0.55 MPa, the catalyst is BCM catalyst, the external electron donor is diisopropyl dimethoxysilane, the propylene homopolymerization time is 30 minutes, the ethylene-propylene copolymerization time is 120 minutes, and other polymerization conditions are the same as in Example 3. Finally, 632 grams of impact copolymer polypropylene is 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 is not started and the polymerization kettle gas outlet is closed, other polymerization conditions are the same as in Example 1. Finally, 267 grams of impact copolymer polypropylene is obtained. The polymer is analyzed and tested, and the ethylene mass content is 9.50%, and the rubber phase mass content is 24.35%. The relevant experimental results are shown in Table 1.

[0052] Comparative Example 2

[0053] Except that the circulating compressor is not started and the polymerization kettle gas outlet is closed, other polymerization conditions are the same as in Example 2. Finally, 394 grams of impact copolymer polypropylene is obtained. The polymer is analyzed and tested, and the ethylene mass content is 4.11%, and the rubber phase mass content is 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 in the gas sample analyzed by chromatography.

[0057] As shown in Table 1, the olefin gas-phase copolymerization system and method of the present application can make the E / P fluctuation range less than 15%, effectively control the gas composition in the polymerization reactor during copolymerization, and produce copolymer products with stable composition. When the gas amount / polymerization amount (A / B, mol / mol) is greater than 5.0 and the volume ratio of the gas tank to the polymerization reactor is greater than 5.0, the gas-phase copolymerization process can make the gas composition fluctuation range in the polymerization reactor at the beginning and end of copolymerization less than 10%. In a more preferred case (e.g., Examples 1 and 3), when the gas amount / polymerization amount (A / B, mol / mol) is greater than 15 and the volume ratio of the gas tank to the polymerization reactor is greater than 15, the gas-phase copolymerization process can make the gas composition fluctuation range in the polymerization reactor at the beginning and end of copolymerization less than 5%. In contrast, as shown in the Comparative Examples, when there is no gas circulation between the gas tank and the polymerization reactor during copolymerization, the gas composition fluctuation range in the polymerization reactor at the beginning and end of copolymerization is more than 40%, and in this case the structure of the copolymer obtained by polymerization is very uneven, and the product quality and stability are greatly affected.

[0058] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for gas-phase copolymerization of olefins, characterized in that, The system used in this method includes a polymerization reactor, a gas distribution tank, and a circulating compressor. The gas inlet of the polymerization reactor is connected to the gas outlet of the gas distribution tank via an inlet pipeline, and the gas outlet of the polymerization reactor is connected to the gas distribution tank via a circulating gas pipeline. The circulating compressor is located on the inlet pipeline or the circulating gas pipeline. The method includes: 1) Prepare a mixed gas containing copolymerized olefins in a gas mixing tank. 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 reactor. The copolymerization olefin gas is introduced into the polymerization reactor, and the gas is circulated between the polymerization reactor and the gas distribution tank through a circulating compressor. The copolymerization reaction takes place in the polymerization reactor. 3) After the copolymerization reaction is completed, the gas circulation is stopped, and the unreacted monomers in the polymerization reactor are recovered. The total amount of olefins consumed in the copolymerization is B mol, and the A / B ratio is greater than 4.

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

3. The olefin gas-phase copolymerization method according to claim 2, wherein, The volume ratio of the gas distribution tank to the polymerization reactor is not less than 15.

4. The olefin gas-phase copolymerization method according to claim 3, wherein, The volume ratio of the gas distribution tank to the polymerization reactor is not less than 20.

5. The olefin gas-phase copolymerization method according to claim 1, wherein, The circulating compressor is located on the inlet pipeline, and a first pressure control unit is provided on the circulating gas 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 gauge signal of the polymerization reactor.

6. The olefin gas-phase copolymerization method according to claim 1, wherein, The circulating compressor is located on the circulating gas pipeline, and a second pressure control unit is provided on the inlet gas pipeline. The second pressure control unit is a second regulating valve or a pressure reducing valve, and the second regulating valve is electrically connected to the pressure gauge signal of the polymerization reactor.

7. The olefin gas-phase copolymerization method according to claim 1, wherein, A / B is greater than 5.

8. The olefin vapor-phase copolymerization method according to claim 7, wherein, A / B is greater than 10.

9. The method for olefin gas-phase copolymerization according to claim 1, wherein, The copolymerized olefin is selected from at least two of ethylene, propylene, and α-olefins containing 4 to 10 carbon atoms.

10. The method for olefin gas-phase copolymerization according to claim 1, wherein, The gas mixture also contains one or more of hydrogen, alkanes, and inert gases.

11. The method for olefin gas-phase copolymerization according to claim 1, wherein, The conditions for copolymerization include: copolymerization temperature of 10~100℃, copolymerization pressure of 0.1~10MPa, and copolymerization time of 1~10000min.

12. The olefin gas-phase copolymerization method according to claim 1, wherein, A homopolymerization stage precedes the olefin gas-phase copolymerization stage.

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