A process for the preparation of polypropylene

Abstract

The application discloses a preparation method of polypropylene resin, which removes mist components in two aspects. In the aspect of process, a multi-stage mist component removal process is adopted, i.e., a polymerization / flash evaporation process in step A and a high-temperature hot nitrogen process in step C, so that the mist components in the polypropylene resin can be effectively removed; in the aspect of material, an external electron donor with a flash point of 60-110 DEG C is selected, so that the volatilization in the mist test can be reduced. Moreover, the polypropylene resin after removing the mist components has reduced stress concentration points in the resin matrix, and the impact performance is improved; meanwhile, the volatile inert components can take away the hydrogen gas entrained in the powder, the rubber phase generated in the gas phase reactor has a larger molecular weight, and the impact performance is improved. Therefore, the polypropylene resin disclosed by the application has less mist components and higher impact performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, in particular to a preparation method of polypropylene. BACKGROUND

[0002] In automobile parts, polypropylene materials are widely used in bumpers, mudguards, deflector plates, instrument panels, door panels, pillars and many other systems. When used as automotive interior parts, polypropylene modified materials will emit small molecules and condense on the car glass to "fog", which will seriously affect the driver's vision and driving safety. The existing patents mainly improve the fogging of polypropylene through post-modification, and there are few reports on improving the fogging value of polypropylene through front-end synthesis.

[0003] Chinese patent CN 107337853 B selects a metallocene catalyst and uses water injection and hot air devolatilization process to prepare a low-fogging, low-volatility and low-odor polypropylene composition for automotive interior. Chinese patent CN 111234387 B introduces a carbon-carbon double bond substituted scratch resistant agent into the formula to reduce the influence of its degradation on the fogging value, and realizes the preparation of low-emission scratch-resistant modified polypropylene. Chinese patent CN 114044966 B selects a low-fogging polypropylene resin and adds a benzene propyl triazole light stabilizer and / or a high molecular weight hindered amine light stabilizer and a phosphite antioxidant in the formula to achieve material resistance to wet fogging test. However, there is no report on directly preparing low-fogging and high-impact polypropylene resin by improving the polymerization process.

[0004] The existing technology mainly focuses on low VOC (low odor) polypropylene and its composite materials. However, TVOC mainly tests volatile low molecular weight organic compounds (such as benzene, toluene, xylene, ethylbenzene, styrene, formaldehyde, acetaldehyde, etc.) collected by TENAX tube at 65℃, which will not adhere to the glass sheet; odor is mainly perceived by the tester through nose whether the odor of polypropylene resin stored at 80℃ for 2h is disturbing, and the resin is rated. The fogging value of the gloss method is the difference in gloss caused by medium and low molecular weight volatile substances (such as oleic acid amide, siloxane, 3,5-di-tert-butyl-4-phenol hydroxyl-benzene propionic acid methyl ester, small molecule alkanes, etc.) condensed on the glass sheet at 100℃, and the fogging value FV is obtained. It can be seen that the two are essentially different.

[0005] At the same time, VOC and odor patents mainly focus on controlling low molecular weight substances remaining in polypropylene and adsorbing odor molecules, but are not suitable for reducing the fogging value. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of polypropylene with low fogging value and good impact resistance.

[0007] The application is realized by the following technical scheme:

[0008] A preparation method of polypropylene, comprising the following steps:

[0009] Step A: the main catalyst, the cocatalyst and the external electron donor are mixed and then introduced into a prepolymerization reactor together with propylene to perform a prepolymerization reaction to obtain a polypropylene prepolymer; then the polypropylene prepolymer is introduced into a loop reactor (which can be one or two loop reactors connected in series or in parallel) together with propylene and hydrogen to perform a polymerization reaction; then the slurry flowing out of the loop reactor is introduced into a high-pressure flash tank after being inactivated on the surface of an activity inhibitor to perform a high-pressure flash process, and liquefied liquefied gas is introduced into the bottom of the high-pressure flash tank to obtain polypropylene powder;

[0010] Step C: the polypropylene powder is introduced into a low-pressure flash tank to further remove volatile components, and then introduced into a steaming tank to inactivate the catalyst / cocatalyst activity in the powder by using high-temperature steam, and then introduced into a drying tank to evaporate the water entrained in the powder by using nitrogen, and then sent to the extrusion material forming discharge port;

[0011] Step D: the polypropylene powder of step C is extruded, formed into material, dried and cut into particles to obtain polypropylene resin.

[0012] The above method is a preparation method of homopolymer polypropylene, if random copolymer polypropylene is prepared, ethylene is contained in the polymerization reaction process of step A, and the addition amount of ethylene is 1-15wt% of the addition amount of propylene in the polymerization reaction process.

[0013] If block copolymer polypropylene is prepared, step B is further included between step A and step C: the polypropylene powder, propylene, ethylene and hydrogen are introduced into a gas phase reactor, an activity inhibitor is added into the gas phase reactor, and a gas phase reaction is performed; wherein, the reaction temperature of the gas phase reaction is 70-90℃, the reaction pressure is 1-2MPa, the volume ratio of ethylene to (ethylene plus propylene) is 0.2-0.5, and the volume ratio of hydrogen to ethylene is 0.001-0.2.

[0014] Specifically, in step A, the prepolymerization reaction conditions are temperature 10-20℃, pressure 3-5MPa, slurry concentration of the main catalyst 150-250g / L (the solution is a mixture of white oil and n-hexane, volume ratio 1:(1-5)), volume flow rate 2-8L / h, mass ratio of the amount of the cocatalyst added to the amount of propylene added in the polymerization reaction process 0.00003-0.0003, mass ratio of the amount of the cocatalyst added to the amount of the external electron donor added 2-80, and the prepolymerization reaction is ended when the D50 particle size of the polypropylene prepolymer is 3-10 times the D50 particle size of the main catalyst; the polymerization reaction conditions are temperature 60-75℃, pressure 3-5MPa, hydrogen concentration in the loop 300-6000ppm (preferably 1000-4000ppm), and the polymerization reaction is ended when the D50 particle size of the polypropylene powder is 30-50 times the D50 particle size of the main catalyst; the high-pressure flash evaporation conditions are pressure 1-2.5MPa, temperature 70-85℃.

[0015] Preferably, in step A, the high-pressure flash evaporation conditions are 1.5-2.0MPa, 70-80℃.

[0016] In step A, the main catalyst has a titanium content of 2-5wt%, a magnesium content of 15-20wt%, and a D50 particle size of 30-70nm.

[0017] In step A, the cocatalyst is at least one selected from triethylaluminum, triisobutylaluminum, methylaluminoxane, tris(pentafluorophenyl)boron, triphenylcarbenium tetrakis(pentafluorophenyl)borate, and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate.

[0018] In step A, the external electron donor has a flash point of 60-110℃, preferably 65-80℃, and optionally, the external electron donor is at least one selected from diisobutyl dimethoxysilane (flash point 68℃), cyclohexylmethyldimethoxysilane (flash point 76℃), and dicyclopentyl dimethoxysilane (flash point 102℃).

[0019] In step A, the activity inhibitor is at least one selected from hydroxyethyl alkyl amine, glycerol monostearate, N,N-dihydroxyethyl lauryl amide, and octadecyl trimethylammonium lactone.

[0020] Wherein, in step A, the liquefied gas is selected from at least one of ethane, propane, cyclopropane, preferably at least one of ethane, propane, and more preferably ethane. The liquefied liquefied gas can be instantaneously vaporized to take away heat after entering the high-pressure flash tank, extremely quickly reduce the temperature of the polypropylene particles in contact with the liquefied gas, and retain the activity of the unreacted catalyst; second, if a part of the liquefied liquefied gas is not instantaneously vaporized, the formed liquid component can form a state similar to a liquid seal, better isolating the hydrogen. The amount of liquefied gas added is 0.1wt% to 5wt% of the total amount of propylene added in the polymerization stage.

[0021] Wherein, in step C, the conditions of the low-pressure flash tank are a pressure of 0.06-0.15MPa, an operating temperature of 70-90℃, and a material level control of 40-80%, preferably a pressure of 0.09-0.11MPa, an operating temperature of 75-85℃, and a material level control of 50-70%. The lower the pressure of the flash tank, the higher the temperature, and the higher the material level, the more obvious the removal of impurities, but the pressure needs to be ensured to be positive pressure, and to ensure the transportation of the material to the rear system, the pressure needs to be higher than the pressure of the rear system, and the operating temperature should not be too high to prevent the low-melting-point PP generated during the copolymerization from caking.

[0022] Wherein, in step C, the conditions of the low-pressure flash tank are a pressure of 0.06-0.15MPa, an operating temperature of 70-90℃, and a material level control of 40-80%, preferably a pressure of 0.09-0.11MPa, an operating temperature of 75-85℃, and a material level control of 50-70%. The lower the pressure of the flash tank, the higher the temperature, and the higher the material level, the more obvious the removal of impurities, but the pressure needs to be ensured to be positive pressure, and to ensure the transportation of the material to the rear system, the pressure needs to be higher than the pressure of the rear system, and the operating temperature should not be too high to prevent the low-melting-point PP generated during the copolymerization from caking.

[0023] Wherein, in step C, the conditions of the low-pressure flash tank are a pressure of 0.06-0.15MPa, an operating temperature of 70-90℃, and a material level control of 40-80%, preferably a pressure of 0.09-0.11MPa, an operating temperature of 75-85℃, and a material level control of 50-70%. The lower the pressure of the flash tank, the higher the temperature, and the higher the material level, the more obvious the removal of impurities, but the pressure needs to be ensured to be positive pressure, and to ensure the transportation of the material to the rear system, the pressure needs to be higher than the pressure of the rear system, and the operating temperature should not be too high to prevent the low-melting-point PP generated during the copolymerization from caking.

[0024] In step D, an auxiliary agent can also be added together with the polypropylene powder to be extruded, formed, dried, and pelletized. The auxiliary agent is selected from antioxidants, lubricants, nucleating agents, etc.

[0025] The present application has the following beneficial effects:

[0026] The present application can remove misting substances in multiple processes, and can obtain a higher impact resistance polypropylene product by introducing liquefied liquefied gas at the bottom of the high-pressure flash tank in the later stage of step A of prepolymerization, adjusting the conditions of the high-pressure flash tank, adjusting the process conditions of the low-pressure flash tank and the steaming tank in step C, and selecting an external electron donor with a high flash point in step A. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 : The schematic diagram of the preparation process equipment for producing block copolymer polypropylene in the present application, 1. Pre-contact tank, 2. Prepolymerization reactor, 3. Loop reactor, 4. High-pressure flash tank, 5. Cyclone separator-1, 6. Gas phase reactor, 7. Low-pressure flash tank, 8. Ethylene propylene separation column, 9. Steaming tank, 10. Powder drying tank, 11. Metering scale, 12. Extrusion granulator, 13. Granule dryer, 14. Elutriator, 15. Cyclone separator-2, 16. Blower, 17. Heat exchanger, 18. Factory air filter, 19. Granule storage tank, 20. Packaging and labeling machine, 21. Light component propylene separation column, 22. Propylene pressurizing pump. DETAILED DESCRIPTION

[0028] The present application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0029] The raw materials used in the examples and comparative examples of the present application are as follows:

[0030] Ethylene, propylene: purity > 99.5%, commercially available;

[0031] External electron donor A: diisobutyl dimethoxysilane, flash point 68℃, commercially available;

[0032] External electron donor B: cyclohexyl methyl dimethoxysilane, flash point 76℃, commercially available;

[0033] External electron donor C: dicyclopentyl dimethoxysilane, flash point 102℃, commercially available;

[0034] External electron donor D: diisopropyl dimethoxysilane, flash point 45℃, commercially available;

[0035] External electron donor E: n-propyl trimethoxysilane, flash point 40.6℃, commercially available;

[0036] External electron donor F: diphenyl dimethoxysilane, flash point 159.1 degrees.

[0037] Main catalyst: titanium content 2.5wt%, magnesium content 19.5wt%, D50 particle size 39nm, and prepared into main catalyst slurry with a concentration of 190g / L;

[0038] Co-catalyst A: triethylaluminum, commercially available;

[0039] Co-catalyst B: methylaluminoxane, commercially available;

[0040] Activity inhibitor: glycerol monostearate, commercially available;

[0041] Liquefied gas: ethane, propane, cyclopropane, purity >99.5%, commercially available;

[0042] Antioxidant: JYANOX-1010 Beijing Jiyi Holdings Group Co., Ltd.;

[0043] Nucleating agent: HPN-20E, Milliken Company;

[0044] Preparation method of polypropylene in the example: Step A: the main catalyst slurry (volume flow rate is 4L / h), co-catalyst (the mass ratio of the amount of co-catalyst added to the amount of propylene added in the polymerization process is 0.0001, and the selection of co-catalyst is shown in the table), external electron donor (the mass ratio of the amount of co-catalyst added to the amount of external electron donor added is 33, and the selection of external electron donor is shown in the table) are mixed in a pre-contact tank and then introduced into a pre-polymerization reactor together with propylene to carry out pre-polymerization reaction to obtain polypropylene prepolymer. The pre-polymerization reaction conditions are shown in the table (temperature, pressure). When the D50 particle size of the polypropylene prepolymer is about 5 times the D50 particle size of the main catalyst, the pre-polymerization reaction is completed. Then the polypropylene prepolymer is introduced into a loop reactor together with propylene (when preparing random copolymer polypropylene, the polymerization reaction stage contains ethylene, and the ethylene content is shown in the table as a percentage of the amount of propylene added in the polymerization process) to carry out polymerization reaction. The polymerization reaction conditions are shown in the table (temperature, pressure, hydrogen concentration in the loop). When the D50 particle size of the polypropylene powder is about 40 times the D50 particle size of the main catalyst, the polymerization reaction is completed. The slurry from the loop reactor is deactivated by an activity inhibitor and then introduced into a high-pressure flash tank to carry out a high-pressure flash process. At the same time, liquefied (or gasified in Comparative Example 4) liquefied gas is introduced into the bottom of the high-pressure flash tank. The high-pressure flash conditions are shown in the table (pressure, temperature). Polypropylene powder is obtained;

[0045] Step B: when the polypropylene is block copolymer polypropylene (in this case, no ethylene is added in Step A), the polypropylene powder obtained in Step A, propylene, and ethylene are introduced into a gas phase reactor, an activity inhibitor is added in the gas phase reactor, and gas phase reaction is carried out. The gas phase reaction conditions are shown in the table (reaction temperature, reaction pressure, volume ratio of ethylene to (ethylene plus propylene), volume ratio of hydrogen to ethylene);

[0046] Step C: The polypropylene powder of Step B is further removed from the volatile components into a low-pressure flash tank (the pressure, temperature, and material level of the low-pressure flash tank are shown in the table), and then into a steaming tank to inactivate the catalyst / co-catalyst activity in the powder with high-temperature steam (steam temperature 130°C) (the pressure, temperature, and material level of the steaming tank), and then into a drying tank to evaporate the water entrained in the powder with nitrogen, and then sent to the extrusion material discharge port (the pressure of the drying tank is about 0.02 MPa, the operating temperature is 80-85°C, the material level is controlled at 70-90%, and the temperature of the nitrogen gas introduced is controlled at 25-35°C).

[0047] Step D: The polypropylene powder of Step C is added into an extrusion granulator with additives in a proportion (shown in the table), and after extrusion, material preparation, drying, and pelletizing, the polypropylene resin is obtained.

[0048] Test methods:

[0049] (1) Ethylene content in polypropylene product: determined by infrared spectroscopy (IR) method.

[0050] (2) Melt mass flow rate: determined according to the test method of GBT 3682.1-2018 at 230°C under a load of 2.16 kg.

[0051] (3) Notched Izod impact performance: determined according to the test method of GBT 1843-2008.

[0052] (4) Hazing value: detected according to the standard of TSM0503G-2013 composite test B method for gloss retention rate. The higher the gloss retention rate, the lower the hazing value.

[0053] Table 1: Preparation process of polypropylene and product test results of examples and comparative examples

[0054]

[0055]

[0056] From Examples 1 / 4 / 5, it is known that the flash point of the external electron donor is preferably 60-90°C, and more preferably 65-80°C.

[0057]

[0058] From Examples 1 / 6 / 7, it is known that the liquefied liquefied gas is preferably ethane, propane, and more preferably ethane.

[0059] From Examples 1 / 8 / 9 / 10 / 11, it is known that the conditions for high-pressure flashing are preferably 1.5-2.0 MPa and 70-80°C.

[0060] Table 1 (continued):

[0061]

[0062] From Example 1 / 8 / 9 / 12 / 13, it is preferred that the high pressure flash conditions are 1.5-2.0 MPa, 70-80°C.

[0063] From Example 1 / 14 / 15 / 16 / 17, it is preferred that the operating conditions of Step C are lower in mist former and higher in impact strength.

[0064] Table 1 (continued):

[0065]

[0066] From Comparative Examples 1-3 versus Example 1-3, it is shown that without the liquefied gas of the invention, the mist former content is high and the impact strength is significantly lower.

[0067] From Comparative Example 4, it is shown that if only gaseous ethane is passed into the high pressure flash tank, the removal of mist former is not significant.

[0068] From Comparative Examples 5 / 6, it is shown that if an external electron donor with a low flash point is selected, the external electron donor is more easily detected in the haze test, the mist former content is high, and the mechanical properties are low.

[0069] From Comparative Example 7, it is shown that if an external electron donor with a too high flash point is selected, the flash cannot take away the external electron donor sufficiently, the mist former content is high, and the mechanical properties are also low.

Claims

1. A process for the preparation of polypropylene, characterized in that, The method comprises the following steps: Step A: the main catalyst, cocatalyst and external electron donor with a flash point of 60-110℃ are mixed and then introduced into a prepolymerization reactor together with propylene to perform a prepolymerization reaction to obtain a polypropylene prepolymer; the polypropylene prepolymer is then introduced into a loop reactor together with propylene and hydrogen to perform a polymerization reaction; the slurry flowing out of the loop reactor is then introduced into a high-pressure flash tank after being surface-inactivated by an activity inhibitor to perform a high-pressure flash process, and liquefied liquefied gas is introduced into the bottom of the high-pressure flash tank to obtain polypropylene powder, the high-pressure flash process being performed at a pressure of 1.5-2.0 MPa and a temperature of 70-80℃; the liquefied gas is selected from at least one of ethane, propane and cyclopropane, and the amount of the liquefied gas added is 0.1 wt%-5 wt% of the total weight of propylene added in the polymerization stage; Step C: the polypropylene powder is introduced into a low-pressure flash tank to further remove volatile components, then introduced into a steaming tank to inactivate the catalyst and cocatalyst in the powder by high-temperature steam, and then introduced into a drying tank to evaporate the water entrained in the powder by nitrogen, and finally sent to the extrusion material forming discharge port; the low-pressure flash tank is operated at a pressure of 0.06-0.15 MPa and a temperature of 70-90℃, and the material level is controlled at 40-80%; the steaming tank is operated at a pressure of 0.01-0.1 MPa and a temperature of 105-130℃, and the material level is controlled at 50-90%, and the steam temperature is 100-140℃; Step D: the polypropylene powder of Step C is extruded, formed into material, dried and cut into particles to obtain polypropylene resin.

2. The process for the preparation of polypropylene according to claim 1, characterized in that, When the polypropylene is a random copolymer polypropylene, the polymerization reaction of Step A contains ethylene, and the amount of ethylene added is 1 wt%-15 wt% of the amount of propylene added in the polymerization reaction.

3. The process for the preparation of polypropylene according to claim 1, characterized in that, When the polypropylene is a block copolymer polypropylene, Step B is further included between Step A and Step C: the polypropylene powder, propylene, ethylene and hydrogen are introduced into a gas phase reactor, an activity inhibitor is added into the gas phase reactor, and a gas phase reaction is performed; wherein, the gas phase reaction is performed at a temperature of 70-90℃ and a pressure of 1-2 MPa, the volume ratio of ethylene to (ethylene plus propylene) is 0.2-0.5, and the volume ratio of hydrogen to ethylene is 0.001-0.

2.

4. The process for the preparation of polypropylene according to claim 1, characterized in that, In Step A, the prepolymerization reaction is performed at a temperature of 10-20℃ and a pressure of 3-5 MPa, the slurry concentration of the main catalyst is 150-250 g / L, the volume flow rate is 2-8 L / h, the mass ratio of the amount of the cocatalyst added to the amount of propylene added in the polymerization reaction is 0.00003-0.0003, the mass ratio of the amount of the cocatalyst added to the amount of the external electron donor added is 2-80, and the prepolymerization reaction is ended when the D50 particle size of the polypropylene prepolymer is 3-10 times the D50 particle size of the main catalyst; the polymerization reaction is performed at a temperature of 60-75℃ and a pressure of 3-5 MPa, the hydrogen concentration in the loop is 300-6000 ppm, and the polymerization reaction is ended when the D50 particle size of the polypropylene powder is 30-50 times the D50 particle size of the main catalyst; the high-pressure flash is performed at a pressure of 1-2.5 MPa and a temperature of 70-85℃.

5. The process for the preparation of polypropylene according to claim 1, characterized in that, In step A, the titanium content of the procatalyst is 2-5 wt%, the magnesium content is 15-20 wt%, the D50 particle size is 30-70 nm; the cocatalyst is selected from at least one of triethylaluminum, triisobutylaluminum, methylaluminoxane, tris(pentafluorophenyl)boron, triphenylcarbenium tetrakis(pentafluorophenyl)borate, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate; the external electron donor has a flash point of 65-80℃, and is selected from at least one of diisobutyl dimethoxysilane, cyclohexylmethyldimethoxysilane, dicyclopentyl dimethoxysilane; the activity inhibitor is selected from at least one of hydroxyethyl alkyl amine, glycerol monostearate, N,N-dihydroxyethyl laurylamide.

6. The process for the preparation of polypropylene according to claim 1, characterized in that, In step A, the liquefied gas is selected from at least one of ethane and propane.

7. The process for the preparation of polypropylene according to claim 1, characterized in that, In step A, the liquefied gas is selected from ethane.

8. The process for the preparation of polypropylene according to claim 1, characterized in that, In step C, the conditions of the low-pressure flash tank are that the pressure is 0.09-0.11 MPa, the operating temperature is 75-85℃, and the material level is controlled at 50-70%; the conditions of the steaming tank are that the pressure is 0.02-0.05 MPa, the operating temperature is 105-110℃, and the material level is controlled at 70-85%.

9. The process for the preparation of polypropylene according to claim 1, characterized in that, In step C, the conditions of the drying tank are that the pressure is 0.005-0.05 MPa, the operating temperature is 75-100℃, the material level is controlled at 70-90%, and the temperature of the nitrogen gas introduced is controlled at 0-110℃.

10. The process for the preparation of polypropylene according to claim 1, characterized in that, In step D, an auxiliary agent can also be added, and the polypropylene powder is extruded, formed, dried, and cut into particles.

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