Preparation method of polypropylene

Abstract

The invention discloses a preparation method of polypropylene resin. Fogging components are removed from the following two aspects. In the aspect of working procedures, a multi-stage fogging component removal working procedure is adopted, namely a polymerization / flash evaporation working procedure in the step A and a high-temperature hot nitrogen working procedure in the step C, and the fogging components in the polypropylene resin can be effectively removed through the working procedures; in the aspect of materials, an external electron donor with a flash point of 60-110 DEG C is selected, so that volatilization in a fogging test can be reduced. In addition, the impact performance of the polypropylene resin with the fogging component removed is improved due to the fact that stress concentration points in a resin matrix of the polypropylene resin are reduced; meanwhile, the volatile inert components take away hydrogen entrained in the powder, the molecular weight of a rubber phase generated by the gas phase reactor is larger, and the impact performance is improved. The polypropylene resin provided by the invention not only has few fogging components, but also has higher impact property.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a method for preparing polypropylene. Background Art

[0002] Among automotive parts, polypropylene materials are widely used in bumpers, fenders, deflectors, dashboards, 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. Existing patents mainly improve the atomization of polypropylene through rear-end modification, and there are few reports on improving the atomization value of polypropylene through front-end synthesis.

[0003] Chinese patent CN 107337853 B uses metallocene catalysts, water injection, and hot air devolatilization to prepare a polypropylene composition for automotive interior with low fogging value, low volatility, and low odor. Chinese patent CN 111234387B reduces the impact of its degradation on the fogging value by introducing a scratch-resistant agent with substituted carbon-carbon double bonds into the formula, thereby achieving the preparation of low-emission scratch-resistant modified polypropylene. Chinese patent CN 114044966B uses low-fogging polypropylene resin, and adds benzotriazole light stabilizers and / or high molecular weight hindered amine light stabilizers and phosphite antioxidants to the formula to achieve the material's anti-wet fogging test. However, there is no report on the method of directly preparing low-fogging 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 tubes at 65°C. These low-molecular-weight organic compounds will not adhere to the glass sheet; the odor is mainly detected by the tester's nose to see whether the odor of polypropylene resin after being stored at 80°C for 2 hours is disturbing, and the resin is rated. The fogging value of the glossiness method tests the glossiness difference caused by low-molecular-weight volatile substances (such as oleamide, siloxane, 3,5-di-tert-butyl-4-phenolhydroxy-phenylpropionic acid methyl ester, small molecule alkanes, etc.) condensed on the glass sheet at 100°C, 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 are mainly focused on controlling low molecular weight substances remaining in polypropylene and adsorbing odor molecules, but are not suitable for reducing atomization values. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing polypropylene with low atomization value and good impact resistance.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for preparing polypropylene comprises the following steps:

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

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

[0011] Step D: The polypropylene powder of step C is extruded, made into a material, dried and pelletized to obtain a polypropylene resin.

[0012] The above method is a method for preparing homopolypropylene. If random copolymer polypropylene is to be prepared, the polymerization reaction process of step A contains ethylene, and the amount of ethylene added is 1-15wt% of the amount of propylene added in the polymerization reaction process.

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

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

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

[0016] Wherein, 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] Wherein, in step A, the co-catalyst is selected from at least one of triethylaluminum, triisobutylaluminum, methylaluminoxane, tris(pentafluorophenylboron), triphenylcarbonium tetrakis(pentafluorophenyl)borate, and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate;

[0018] Wherein, in step A, the flash point of the external electron donor is 60-110° C., preferably 65-80° C., and optionally, the external electron donor is selected from at least one of diisobutyldimethoxysilane (flash point 68° C.), cyclohexylmethyldimethoxysilane (flash point 76° C.), and dicyclopentyldimethoxysilane (flash point 102° C.);

[0019] Wherein, in step A, the activity inhibitor is selected from at least one of hydroxyethyl alkylamine, glycerol monostearate, N,N-dihydroxyethyl lauramide, and octadecyl trimethyl ammonium betaine;

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

[0021] Among them, in step C, the conditions of the low-pressure flash tank are pressure 0.06-0.15MPa, operating temperature 70-90°C, material level control at 40-80%, preferably, pressure 0.09-0.11MPa, operating temperature 75-85°C, material level control at 50-70%. The lower the pressure of the flash tank, the higher the temperature, the higher the material level, the more obvious the removal of impurities, but the pressure must be positive, and to ensure that the material is transported backward, the pressure must be higher than the pressure of the subsequent system, and the operating temperature should not be too high to prevent the low-melting-point PP generated during the copolymerization reaction from agglomerating here.

[0022] Among them, in step C, the conditions of the steamer are as follows: the pressure is 0.01-0.1MPa, the operating temperature is 105-130°C, the material level is controlled at 50-90%, and the steam temperature range is 100-140°C. Preferably, the pressure is 0.02-0.05MPa, the operating temperature is 105-110°C, and the material level is controlled at 70-85%. The pressure of the steamer needs to be between the normal pressure and the low-pressure flash tank, and the lower the better. The operating temperature needs to exceed 105°C to ensure that the water is in a vapor state, but the temperature should not be too high to prevent PP powder from agglomerating. The higher the material level, the more obvious the removal of impurities.

[0023] Wherein, in step C, the conditions of the drying tank are as follows: pressure 0.005-0.05 MPa, operating temperature 75-100°C, material level controlled at 70-90%, and temperature of the nitrogen introduced controlled at 0-110°C.

[0024] In step D, an auxiliary agent may be added to the polypropylene powder for extrusion, material preparation, drying and pelletization. The auxiliary agent is selected from antioxidants, lubricants, nucleating agents and the like.

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

[0026] The present invention mainly introduces liquefied gas into the bottom of a high-pressure flash tank in the late stage of prepolymerization in step A and adjusts the conditions of the high-pressure flash tank. In step C, the process conditions of a low-pressure flash tank and a steam tank are adjusted to further remove volatile components. In step A, an external electron donor with a high flash point is selected, so that fogging substances can be removed in multiple processes and a polypropylene product with higher impact resistance can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 : Schematic diagram of the preparation process equipment for producing block copolymer polypropylene of the present invention, 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 tower, 9. steam tank, 10. powder drying tank, 11. weighing scale, 12. extrusion granulator, 13. pellet dryer, 14. elutriator, 15. cyclone separator-2, 16. blower, 17. heat exchanger, 18. factory air filter, 19. pellet storage tank, 20. packaging stacker, 21. light component propylene separation tower, 22. propylene pressure pump. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

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

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

[0031] External electron donor A: diisobutyldimethoxysilane, flash point 68°C, commercially available;

[0032] External electron donor B: cyclohexylmethyldimethoxysilane, flash point 76°C, commercially available;

[0033] External electron donor C: dicyclopentyldimethoxysilane, flash point 102°C, commercially available;

[0034] External electron donor D: diisopropyldimethoxysilane, flash point 45°C, commercially available;

[0035] External electron donor E: n-propyltrimethoxysilane, flash point 40.6°C, commercially available;

[0036] External electron donor F: diphenyldimethoxysilane, 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] Cocatalyst B: methylaluminoxane, commercially available;

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

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

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

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

[0044] Preparation method of polypropylene in the embodiment: Step A: The main catalyst slurry (volume flow rate is 4 L / h), the co-catalyst (the mass ratio of the amount of the co-catalyst added to the amount of propylene added in the polymerization reaction process is 0.0001, and the selection of the co-catalyst is shown in the table), and the external electron donor (the mass ratio of the amount of the co-catalyst added to the amount of the external electron donor added is 33, and the selection of the external electron donor is shown in the table) are mixed in a pre-contact tank and then enter the prepolymerization reactor together with propylene for prepolymerization to obtain a polypropylene prepolymer. The prepolymerization reaction conditions are shown in the table (temperature, pressure). The prepolymerization reaction is terminated when the D50 particle size of the polypropylene prepolymer is about 5 times that of the main catalyst, and then the polypropylene prepolymer is added. The polypropylene powder and propylene enter the loop reactor together for polymerization reaction (when preparing random copolymer polypropylene, ethylene is contained in the polymerization reaction stage, and the ethylene content is the weight percentage of the propylene added in the polymerization process, see the table), 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, and the slurry flowing out of the loop reactor enters the high-pressure flash tank for high-pressure flash process after the surface deactivation of the active inhibitor, and at the same time, liquefied (comparative example 4 is gasified) liquefied gas is introduced into the bottom of the high-pressure flash tank, and the conditions of high-pressure flash are shown in the table (pressure, temperature), to obtain polypropylene powder;

[0045] Step B: When the polypropylene is block copolymer polypropylene (in this case, ethylene is not added in step A), the polypropylene powder, propylene and ethylene obtained in step A are introduced into a gas phase reactor, an activity inhibitor is added into the gas phase reactor, and a gas phase reaction is carried out. The conditions of the gas phase reaction 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 put into a low-pressure flash tank to further remove volatile components (the pressure, temperature and material level of the low-pressure flash tank are shown in the table), and then into a steaming tank, where the activity of the catalyst / co-catalyst in the powder is inactivated with high-temperature steam (steam temperature 130° C.) (steaming tank pressure, temperature and material level), and then into a drying tank, where the water entrained in the powder is evaporated with nitrogen and then sent to the extrusion material discharge port (the pressure of the drying tank is about 0.02MPa, the operating temperature is 80-85° C., the material level is controlled at 70-90%, and the temperature of the nitrogen introduced is controlled at 25-35° C.);

[0047] Step D: Add the polypropylene powder and additives of step C into an extrusion granulator according to a certain proportion (see table), and obtain polypropylene resin after extrusion, material preparation, drying and pelletizing.

[0048] Various test methods:

[0049] (1) Ethylene content in polypropylene products: Determined by infrared spectroscopy (IR).

[0050] (2) Melt mass flow rate: measured according to the test method of GBT3682.1-2018 at 230°C and a load of 2.16 kg.

[0051] (3) Cantilever beam notched impact performance: measured according to the test method of GBT1843-2008.

[0052] (4) Fogging value: The gloss retention rate is tested according to the TSM0503G-2013 composite test method B standard. The higher the gloss retention rate, the lower the fogging value.

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

[0054]

[0055]

[0056] It can be seen from Examples 1 / 4 / 5 that the flash point of the external electron donor is preferably 60-90°C, more preferably 65-80°C.

[0057]

[0058] It can be seen from Examples 1 / 6 / 7 that the liquefied gas is preferably ethane or propane, and more preferably ethane.

[0059] It can be seen from Examples 1 / 8 / 9 / 10 / 11 that the preferred conditions for high-pressure flash evaporation are 1.5-2.0 MPa and 70-80°C.

[0060] Table 1 continued:

[0061]

[0062] It can be seen from Examples 1 / 8 / 9 / 12 / 13 that the preferred conditions for high-pressure flash evaporation are 1.5-2.0 MPa and 70-80°C.

[0063] It can be seen from Examples 1 / 14 / 15 / 16 / 17 that under the preferred operating conditions of step C, the fogging component is lower and the impact strength is higher.

[0064] Table 1 continued:

[0065]

[0066] It can be seen from the comparison between Comparative Examples 1-3 and Examples 1-3 that when the liquefied liquefied gas of the present invention is not contained, the content of the mist-forming component is high and the impact strength is significantly reduced.

[0067] It can be seen from Comparative Example 4 that if only ethane in gaseous form is introduced into the high-pressure flash tank, the effect of removing the mist-forming components is not significant.

[0068] It can be seen from Comparative Examples 5 / 6 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 content of fogging components is high, and the mechanical properties are low.

[0069] It can be seen from Comparative Example 7 that when an external electron donor with a flash point that is too high is selected, flash evaporation cannot fully carry away the external electron donor, the content of fogging components is high, and the mechanical properties are also low.

Claims

1. A method for preparing polypropylene, characterized in that: The following steps are involved: Step A: mixing the main catalyst, the co-catalyst and the external electron donor and introducing them into a prepolymerization reactor together with propylene for prepolymerization to obtain a polypropylene prepolymer; Then the polypropylene prepolymer, propylene and hydrogen are introduced into the loop reactor for polymerization reaction; then the slurry flowing out of the loop reactor is deactivated on the surface of the active inhibitor and then enters the high-pressure flash tank for high-pressure flash process, and liquefied gas is introduced into the bottom of the high-pressure flash tank to obtain polypropylene powder; Step C: The polypropylene powder is put into a low-pressure flash tank to further remove volatile components, then into a steaming tank to inactivate the activity of the catalyst / co-catalyst in the powder with high-temperature steam, then into a drying tank to evaporate the water entrained in the powder with nitrogen and then sent to the extrusion material discharge port; Step D: The polypropylene powder of step C is extruded, made into a material, dried and pelletized to obtain a polypropylene resin.

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

3. The method for preparing polypropylene according to claim 1, characterized in that: When the polypropylene is block copolymer polypropylene, step B is further included between step A and step C: introducing polypropylene powder, propylene, ethylene and hydrogen into a gas phase reactor, adding an activity inhibitor into the gas phase reactor, and conducting a gas phase reaction; wherein the conditions of the gas phase reaction are a reaction temperature of 70-90° C., a reaction pressure of 1-2 MPa, a volume ratio of ethylene to (ethylene plus propylene) of 0.2-0.5, and a volume ratio of hydrogen to ethylene of 0.001-0.

2.

4. The method for preparing polypropylene according to claim 1, characterized in that: In step A, the prepolymerization reaction conditions are as follows: temperature 10-20° C., pressure 3-5 MPa, slurry concentration of the main catalyst 150-250 g / L, volume flow rate 2-8 L / h, mass ratio of the amount of the cocatalyst added to the amount of propylene added in the polymerization reaction 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 ends 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 as follows: temperature 60-75° C., pressure 3-5 MPa, hydrogen concentration in the annular tube 300-6000 ppm, and the polymerization reaction ends when the D50 particle size of the polypropylene powder is 30-50 times the D50 particle size of the main catalyst; and the high-pressure flash evaporation conditions are as follows: pressure 1-2.5 MPa, temperature 70-85° C.

5. The method for preparing polypropylene according to claim 4, characterized in that: In step A, the conditions of high-pressure flash evaporation are 1.5-2.0 MPa and 70-80°C.

6. The method for preparing polypropylene according to claim 1, characterized in that: 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; the co-catalyst is selected from at least one of triethylaluminum, triisobutylaluminum, methylaluminoxane, tris(pentafluorophenylboron), triphenylcarbonium tetrakis(pentafluorophenyl)borate, and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate; the flash point of the external electron donor is 60-110°C, preferably 65-80°C, and the external electron donor is selected from at least one of diisobutyldimethoxysilane, cyclohexylmethyldimethoxysilane, and dicyclopentyldimethoxysilane; the activity inhibitor is selected from at least one of hydroxyethyl alkylamine, glycerol monostearate, N,N-dihydroxyethyl lauramide, and octadecyltrimethylammonium ethyl lactone.

7. The method for preparing polypropylene according to claim 1, characterized in that: In step A, the liquefied gas is selected from at least one of ethane, propane, and cyclopropane, preferably at least one of ethane and propane, and more preferably ethane; the amount of liquefied gas added is 0.1 wt% to 5wt% of the total weight of propylene added in the polymerization reaction stage.

8. The method for preparing polypropylene according to claim 1, characterized in that: In step C, the conditions of the low-pressure flash tank are a pressure of 0.06-0.15 MPa, an operating temperature of 70-90°C, and a material level controlled at 40-80%. Preferably, the pressure is 0.09-0.11 MPa, the operating temperature is 75-85°C, and the material level is controlled at 50-70%; the conditions of the steam tank are a pressure of 0.01-0.1 MPa, an operating temperature of 105-130°C, a material level controlled at 50-90%, and a steam temperature range of 100-140°C. Preferably, the pressure is 0.02-0.05 MPa, the operating temperature is 105-110°C, and the material level is controlled at 70-85%.

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

10. The method for preparing polypropylene according to claim 1, characterized in that: In step D, an auxiliary agent may be added to the polypropylene powder and the mixture is extruded, made into a material, dried and pelletized.

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