Low-VOC (volatile organic compound) polypropylene material and preparation method thereof

Abstract

The invention discloses a low-VOC polypropylene material and a preparation method thereof, and relates to the technical field of high polymer material preparation, and the preparation method comprises the following steps: step S1, roughly removing light components CO and O2; step S2, removing other impurities; step S3, polymerization reaction; step S4, removing residual VOCs (Volatile Organic Compounds) in the polypropylene powder; and S5, removing water, granulating and packaging. The low-VOC polypropylene material prepared by the method disclosed by the invention is good in mechanical property, low in VOC content and good in processing fluidity, and the preparation process is simple and easy to implement.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, and in particular to a low-VOC polypropylene material and a preparation method thereof. Background Art

[0002] Polypropylene is a polymer formed by the addition polymerization of propylene. It is a white waxy material with a transparent and light appearance. It has many excellent comprehensive properties and is widely used in the production of fiber products such as clothing and blankets, medical equipment, automobiles, bicycles, parts, pipelines, chemical containers, etc. It is also used in food and drug packaging. However, polypropylene will produce a certain amount of volatile gas during heating, storage or processing. If polypropylene is used to process automotive interior parts, automobile bumpers, side door panels and other parts, it will inevitably produce odor during use, which will cause certain harm to the health of drivers and passengers in closed compartments, limiting its application in the automotive industry. It is under this situation that low-VOC polypropylene materials came into being, and its appearance has attracted widespread attention in the industry.

[0003] At present, most low-VOC polypropylene materials are modified by adding additives for blending and screw devolatilization to reduce volatiles and odors, but they still cannot meet the concentration requirements of benzene, toluene, xylene, ethylbenzene, styrene, formaldehyde, acetaldehyde, acrolein, etc. in the air inside the car as stipulated in the "Guidelines for Passenger Car Interior Air Quality Assessment" (GB / T 27630-2011), and the modification effect needs to be improved. In addition, due to the compatibility issues between the added additives and the polypropylene substrate, technical defects such as poor mechanical properties, processing fluidity and performance stability of the product are often caused.

[0004] For example, a Chinese invention patent with application publication number CN110157093A discloses a low-odor, low-VOC polypropylene composite material for automotive interior and a preparation method thereof. By adding a deodorant and an extractant, during the plasticizing and granulation process, the microporous structure of the deodorant adsorbs low-molecular volatile substances, and the low-molecular extractant contained in the microporous structure of the deodorant extracts the low-molecular substances at high temperature, and then undergoes subsequent process treatment, and the low-molecular substances are volatilized again through different heating and cooling processes, thereby achieving the low-odor and low-VOC effects of the polypropylene composite material. This method has a complex subsequent heating and cooling process, which results in the VOC not being completely volatilized and still having residues, and therefore has certain limitations.

[0005] It can be seen that the development of a low-VOC polypropylene material and its preparation method with good mechanical properties, low VOC content, good processing fluidity, and simple and easy preparation process meets market demand and is of great significance to promoting the development of the polypropylene material field and realizing green and economical polypropylene production. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a low-VOC polypropylene material having good mechanical properties, low VOC content, good processing fluidity, and a simple and easy preparation process and a preparation method thereof.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a low VOC polypropylene material, comprising the following steps:

[0008] Step S1, roughly removing light components CO and O2: After propylene enters the boundary area of ​​the polypropylene device, it is roughly dehydrated in the coalescer and then enters the propylene degassing tower to roughly remove light components CO and O2;

[0009] Step S2, removing other impurities: the propylene from which the light components CO and O2 are roughly removed in step S1 is sequentially passed through a desulfurizer, a membrane separation dehydrator, a deoxygenator, and a dearsenicizer to remove other impurities;

[0010] Step S3, polymerization reaction: the propylene from which other impurities have been removed in step S2 and the propylene recovered from the propylene recovery unit are pressurized to a certain pressure by a propylene feeding pump and then fed into a polymerization system, a polymerization reaction is carried out in the polymerization system, and the polypropylene powder discharged from the polymerization system carries the propylene into a low-pressure filter under its own pressure for gas-solid separation, and the separated propylene enters the propylene recovery unit;

[0011] Step S4, removal of residual VOCs in polypropylene powder: the separated polypropylene powder is introduced into a heater to remove some VOCs in the polypropylene powder at a certain temperature, and then enters a steam evaporator to remove residual propylene, propane and unreacted catalyst, additive and oil, so as to further reduce the residual VOCs and odor of the polypropylene powder;

[0012] Step S5, dehydration, granulation, and packaging: the polypropylene powder leaving the steamer is sent to a fluidized bed dryer to remove the remaining moisture in the polypropylene powder, and then is conveyed to a silo by nitrogen pressure, and is extruded, granulated, and packaged to obtain a polypropylene material.

[0013] Preferably, the amount of water in the propylene after the crude dehydration in the coalescer in step S1 is ≤3.0×10 - 4 wt%.

[0014] Preferably, the desulfurizer in step S2 can perform organic sulfur hydrolysis desulfurization and fine desulfurization.

[0015] Preferably, the water content of propylene after dehydration by the membrane separation dehydrator in step S2 is ≤2.0×10 -6 wt%.

[0016] Preferably, the certain pressure in step S3 is 4.3 MPa.

[0017] Preferably, the raw materials for the polymerization reaction in step S3 include hydrogen, other olefins and propylene.

[0018] Preferably, the other olefin is at least one of ethylene, butene, hexene and octene.

[0019] Preferably, the polymerization system in step S3 is a production method that adopts a combination of a vertical liquid phase polymerization kettle and a horizontal kettle gas phase polymerization, with a high-efficiency carrier catalyst as the main catalyst, alkyl aluminum as the co-catalyst, silane as the electron donor, hydrogen as the molecular weight regulator, and propylene as the polymerization monomer; prepolymerization, bulk slurry polymerization, and gas phase polymerization are performed successively to obtain polypropylene powder.

[0020] Preferably, the polymerization system in step S3 adopts a multi-stage reactor when producing impact-resistant polypropylene, and the third reactor is connected to the fourth reactor through an air lock to control the reaction pressure, temperature, hydrogen concentration of the third reactor and the reactor pressure and temperature of the fourth reactor.

[0021] Preferably, the certain temperature in step S4 is 110-120°C.

[0022] Preferably, the heating method of the heater in step S4 is electric heating or steam heating.

[0023] Preferably, the steam from the steamer in step S4 enters the steamer in three ways, passes through a steam distributor to ensure that the polypropylene powder in the steamer is fully in contact with the steam, and removes residual propylene, propane and unreacted catalysts, additives and oil. The polypropylene powder flows in the steamer accompanied by the slow rotation of the agitator. Another low-pressure steam is sent to the steamer heating coil to heat the material inside the steamer, so as to better remove the residue and prevent condensation from forming on the inner wall. Under the control of the material level, relying on the action of gravity, the polypropylene powder leaves the steamer from the bottom and enters the fluidized bed dryer.

[0024] Preferably, the total carbon volatility of the polypropylene material in step S5 is less than 50 ug (C) / g.

[0025] Preferably, the fluidized bed dryer in step S5 is a vertical cylindrical structure, with an expanded structure at the top and a sieve plate nitrogen distributor at the bottom; the polypropylene powder enters the fluidized bed dryer from the top, and the hot nitrogen circulates in the nitrogen closed loop and enters the fluidized bed dryer through the sieve plate distributor; the nitrogen and the polypropylene powder are in countercurrent contact; the spiral plate in the fluidized bed dryer causes the powder to move in a piston flow, while removing moisture from the polypropylene powder.

[0026] Preferably, the exhaust section of the extrusion granulation packaging in step S5 is at the filter where the extruder feed hopper and the mixer flange are connected, and the residual VOCs and residual odor in the polypropylene are extracted through a vacuum exhaust device, and the vacuum pump controls the inlet pressure to -30 to -10 kPa.

[0027] Due to the application of the above technical solution, the present invention has the following beneficial effects:

[0028] (1) The method for preparing the low-VOC polypropylene material disclosed in the present invention has simple process operation, high production rate, low investment, and is easy to promote and apply; the prepared low-VOC polypropylene material has a low organic volatile matter content, high fluidity and very good impact resistance.

[0029] (2) The low VOC polypropylene material disclosed in the present invention uses membrane separation technology to remove trace moisture to improve the isotacticity of polypropylene (more than 96%), avoid the phenomenon of sticking to the kettle due to low isotacticity of polypropylene, make it difficult to discharge materials, and affect the operation of the device; at the same time, the water content exceeds the standard, and the amount of alkyl aluminum needs to be increased to maintain the normal operation of the polypropylene production device, resulting in high ash content in the final product, increased catalyst numbers and reduced product quality. Conventional silica gel / molecular sieve adsorption technology must be switched off for 4 to 8 hours of regeneration after the silica gel / molecular sieve is saturated with adsorption. During regeneration, the nitrogen at room temperature must be electrically heated to 420°C, the silica gel / molecular sieve tower must be heated to more than 250°C, and the temperature must be kept constant for 4 hours, which consumes a lot of electricity; and in order to balance the pressure balance of the adsorption tower and the recovery tower, the propylene in the absorption tower can only be discharged, resulting in a large waste of propylene; the absorption / regeneration refining system is complex, the process flow is long, and the investment is large. Compared with silica gel / molecular sieve adsorption technology, membrane separation technology for removing trace water has the advantages of low energy consumption (except for the power consumption of the vacuum pump, there is no gas energy consumption, and the energy consumption is reduced by more than 95%), less propylene waste (except for a small amount of propylene escaping with water molecules, there is no loss), simple process flow and low investment.

[0030] (3) The low VOC polypropylene material disclosed in the present invention, the catalyst, co-catalyst and electron donor added during the propylene polymerization process, and the peroxide added to control the molecular weight of propylene will cause the powder after propylene polymerization to contain a certain amount of VOC. At the same time, the residual unreacted monomers, generated oligomers and residual moisture on the surface and pore size of the polypropylene powder after polymerization. The traditional VOCs removal process is to remove VOCs from polypropylene powder with nitrogen, but this process has high energy consumption, large nitrogen consumption, large air separation processing volume and high investment cost. The VOCs in the polypropylene powder can be reduced from 510ug(C) / g to less than 50ug(C) / g by the devolatilization technology of heating+gas steaming+drying. Finally, the vacuum exhaust device of the extrusion granulation system is used for further treatment to remove VOCs and odor caused by the polypropylene melt and additives. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of a process for preparing a low-VOC polypropylene material according to the present invention;

[0032] Explanation of reference numerals: 1-coalescer; 2-propylene preheater; 3-propylene degassing tower; 4-desulfurizer; 5-membrane separation dehydrator; 6-deoxidizer; 7-arsenic remover; 8-propylene tank; 9-propylene feed pump; 10-prepolymerization kettle; 11-first reactor; 12-first reactor condenser; 13-propylene condensate tank; 14-first reactor circulation fan; 15-third reactor; 16-third reactor condenser; 17-propylene buffer tank 1; 18-propylene condensate pump 1; 19-third reactor circulation fan; 20-gas-solid separator; 21-gas lock; 22-fourth reactor; 23-fourth reactor condenser; 24-propylene buffer tank 2; 25-propylene condensate pump 2; 26-fourth reactor circulation fan; 27-low-pressure filter; 28-heater; 29-steamer; 30-steamer cyclone separator; 31-steamer washing tower; 32-dryer washing tower circulation pump; 33-hydrocarbon water separator; 34-waste white oil barrel; 35-recovery propylene compressor inlet buffer tank; 36-recovery propylene compressor; 37-recovery propylene compressor outlet cooler; 38-recovery propylene tank; 39-dryer; 40-dryer cyclone separator; 41-fine powder discharge hopper; 42-drying nitrogen heater; 43-dryer circulating nitrogen fan; 44-dryer circulating nitrogen fan inlet buffer tank; 45-dryer washing tower; 46-dryer washing tower circulating water cooler; 47-dryer washing tower circulation pump; 48-silo; 49-extrusion granulation; 100-propylene pipeline; 101-slurry pipeline; 102-circulation pipeline; 103-polypropylene slurry pipeline. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only embodiments of a part of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained under the premise of equivalent changes and modifications made by ordinary technicians in the field should belong to the scope of protection of the present invention.

[0034] In the description of the present invention, it should be understood that the instruments, equipment or devices involved are all conventional instruments, equipment or devices unless otherwise specified; the raw materials or compounds involved are all commercially available conventional raw materials or compounds unless otherwise specified; the methods involved are all conventional methods unless otherwise specified.

[0035] Example 1

[0036] like Figure 1 , a method for preparing a low VOC polypropylene material, comprising the following steps:

[0037] (1) After propylene enters the boundary area of ​​the polypropylene device, it is roughly dehydrated by the coalescer and then enters the propylene degassing tower to roughly remove light components such as CO and O2. It then passes through the desulfurizer (including organic sulfur hydrolysis and fine desulfurization), membrane separation dehydrator (water content less than 2ppm), deoxygenator, and dearsenicizer to remove other impurities. The propylene recovered from the high-pressure propylene is pressurized to 4.3MPa(G) by the propylene feeding pump and sent to the polymerization system;

[0038] (2) Low-temperature prepolymerization process is adopted, and two vertical stirring prepolymerization reactors are operated in parallel. The raw materials including main catalyst, co-catalyst, electron donor and propylene enter the vertical prepolymerization reactor with a stirrer for prepolymerization reaction at 15°C and 3MPa(G), and the residence time is 8min. The heat of polymerization reaction is withdrawn by chilled water introduced into the reactor jacket and internal cooling pipe. The catalyst and propylene after prepolymerization enter the first reactor for slurry polymerization by their own pressure; the slurry polymerization is carried out by two vertical stirred polymerization kettles in parallel, and propylene is slurry polymerized in the first reactor at 65°C and 3.0MPa(G) with a residence time of 40min; the heat of polymerization reaction is taken away by the vaporization heat of liquid propylene and jacket cooling water; the slurry and unreacted propylene in the first reactor enter the third reactor for gas phase polymerization by their own pressure under liquid level control; the operating conditions of the third reactor are 80°C, 2.1MPa(G) and a residence time of 35min; the polypropylene powder leaving the third reactor and the carried propylene gas are separated by gas-solid separation, and after separating the carried propylene gas, random / copolymerized polypropylene powder is obtained; the polypropylene powder coming out of the third reactor enters the fourth reactor, the polymerization temperature of the fourth reactor is 60-80°C, the polymerization pressure is 2.2MPa(G), and the polypropylene coming out of the fourth reactor is impact-resistant polypropylene. The polypropylene powder from the polymerization system enters the low-pressure filter for gas-solid separation, and the separated propylene gas enters the propylene recovery unit; the separated polypropylene powder enters the heater and is heated to 110°C, maintained for 15 minutes, and after removing some VOCs in the polypropylene powder, it enters the steamer to remove the residual propylene, propane and unreacted catalysts, additives and oil, further reducing the residual VOCs and odor of the polypropylene powder. The temperature of the polypropylene powder leaving the steamer is 105°C, and it is sent to the fluidized bed dryer to remove the remaining moisture in the polypropylene powder, and then it is sent to the silo through nitrogen pressurized pneumatic conveying. After extrusion granulation and packaging, in the exhaust section of the extrusion granulation packaging, at the filter connected to the extruder feed hopper and the mixer flange, the residual VOCs and residual odor in the polypropylene are extracted through the vacuum exhaust device (residual peroxide <5ppm), and the vacuum pump controls the inlet pressure to -30kPa. Ensure the production of polypropylene materials with a total carbon volatility of <50ug(C) / g.

[0039] Example 2

[0040] like Figure 1 , a method for preparing a low VOC polypropylene material, comprising the following steps:

[0041] (1) After propylene enters the boundary area of ​​the polypropylene unit, it is roughly dehydrated by the coalescer and then enters the propylene degassing tower to roughly remove light components such as CO and O2. It then passes through the desulfurizer (including organic sulfur hydrolysis and fine desulfurization), molecular sieve dehydration tower (water content less than 5ppm), deoxygenator, and dearsenicizer to remove other impurities. The propylene recovered from the high-pressure propylene is pressurized to 4.3MPa(G) by the propylene feeding pump and sent to the polymerization system;

[0042] (2) A low-temperature prepolymerization process is adopted, and two vertical stirring prepolymerization reactors are operated in parallel. The raw materials including the main catalyst, the co-catalyst, the electron donor and propylene enter the vertical prepolymerization reactor with a stirrer for prepolymerization reaction at 20°C and 3.2MPa(G), and the residence time is 9 minutes. The heat of polymerization reaction is withdrawn by the chilled water introduced into the reactor jacket and the inner cooling pipe. The catalyst and propylene after prepolymerization enter the first reactor for slurry polymerization by their own pressure; the slurry polymerization is carried out by two vertical stirring polymerization reactors operated in parallel, and propylene is slurried in the first reactor at 70°C and 3.2MPa(G), and the residence time is 45 minutes. The heat of polymerization reaction is taken away by the vaporization heat of liquid propylene and the jacket cooling water. The slurry and unreacted propylene in the first reactor, relying on their own pressure, enter the third reactor for gas phase polymerization under liquid level control; the operating conditions of the third reactor are 80°C, 2.3MPa(G), and a residence time of 38min; the polypropylene powder leaving the third reactor and the carried propylene gas are separated by gas-solid separation, and after separating the carried propylene gas, random / copolymer polypropylene powder is obtained; the polypropylene powder coming out of the third reactor enters the fourth reactor, the polymerization temperature of the fourth reactor is 65°C, the polymerization pressure is 2.3MPa(G), and the polypropylene coming out of the fourth reactor is impact-resistant polypropylene. The polypropylene powder from the polymerization system enters the low-pressure filter for gas-solid separation, and the separated propylene gas enters the propylene recovery unit; the separated polypropylene powder enters the heater and is heated to 113°C, maintained for 15 minutes, and after removing some VOCs in the polypropylene powder, it enters the steamer to remove the residual propylene, propane and unreacted catalysts, additives and oil, further reducing the residual VOCs and odor of the polypropylene powder. The temperature of the polypropylene powder leaving the steamer is 105°C, and it is sent to the fluidized bed dryer to remove the residual moisture in the polypropylene powder, and then it is sent to the silo through nitrogen pressurized pneumatic conveying. After extrusion granulation and packaging, in the exhaust section of the extrusion granulation packaging, at the filter connected to the extruder feed hopper and the mixer flange, the residual VOCs and residual odor in the polypropylene are extracted through the vacuum exhaust device (residual peroxide <5ppm), and the vacuum pump controls the inlet pressure at -25kPa. Ensure the production of polypropylene materials with a total carbon volatility of <50ug(C) / g.

[0043] Example 3

[0044] like Figure 1 , a method for preparing a low VOC polypropylene material, comprising the following steps:

[0045] (1) After propylene enters the boundary area of ​​the polypropylene device, it is roughly dehydrated by the coalescer and then enters the propylene degassing tower to roughly remove light components such as CO and O2. It then passes through the desulfurizer (including organic sulfur hydrolysis and fine desulfurization), membrane separation dehydrator (water content less than 2ppm), deoxygenator, and dearsenicizer to remove other impurities. The propylene recovered from the high-pressure propylene is pressurized to 4.3MPa(G) by the propylene feeding pump and sent to the polymerization system;

[0046] (2) A low-temperature prepolymerization process is adopted, and two vertical stirring prepolymerization kettles are operated in parallel; the raw materials including the main catalyst, the co-catalyst, the electron donor and propylene enter the vertical prepolymerization kettle with a stirrer for prepolymerization reaction at 24°C and 3.5MPa(G), and the residence time is 10min; the polymerization reaction heat is withdrawn by the chilled water introduced into the reactor jacket and the internal cooling pipe; the catalyst and propylene after prepolymerization enter the first reactor by their own pressure for slurry polymerization; the slurry polymerization is carried out by two vertical stirring polymerization kettles operated in parallel, and propylene is slurried in the first reactor at 72°C and 3.3MPa(G), and the residence time is 50min; the polymerization reaction heat is removed by the liquid phase The propylene vaporization heat and jacket cooling water are taken away; the slurry and unreacted propylene in the first reactor, relying on their own pressure, enter the third reactor for gas phase polymerization under liquid level control; the operating conditions of the third reactor are 80°C, 2.6MPa(G), and a residence time of 40min; the polypropylene powder leaving the third reactor and the carried propylene gas are separated by gas-solid separation, and after separating the carried propylene gas, random / copolymer polypropylene powder is obtained; the polypropylene powder coming out of the third reactor enters the fourth reactor, the polymerization temperature of the fourth reactor is 70°C, the polymerization pressure is 2.4MPa(G), and the polypropylene coming out of the fourth reactor is impact-resistant polypropylene. The polypropylene powder from the polymerization system enters the low-pressure filter for gas-solid separation, and the separated propylene gas enters the propylene recovery unit; the separated polypropylene powder directly enters the steamer to remove the residual propylene, propane and unreacted catalysts, additives and oil, further reducing the residual VOCs and odor of the polypropylene powder. The temperature of the polypropylene powder leaving the steamer is 105°C, and it is sent to the fluidized bed dryer to remove the residual moisture in the polypropylene powder. After being pneumatically conveyed by nitrogen pressure, it is sent to the silo for extrusion granulation and packaging. In the exhaust section of the extrusion granulation packaging, at the filter connected to the extruder feed hopper and the mixer flange, the residual VOCs and residual odor in the polypropylene are extracted through the vacuum exhaust device (residual peroxide <5ppm), and the vacuum pump controls the inlet pressure at -20kPa. Ensure the production of polypropylene materials with a total carbon volatility of <50ug(C) / g.

[0047] Example 4

[0048] like Figure 1 , a method for preparing a low VOC polypropylene material, comprising the following steps:

[0049] (1) After propylene enters the boundary area of ​​the polypropylene unit, it is roughly dehydrated by the coalescer and then enters the propylene degassing tower to roughly remove light components such as CO and O2. It then passes through the desulfurizer (including organic sulfur hydrolysis and fine desulfurization), molecular sieve dehydration tower (water content less than 5ppm), deoxygenator, and dearsenicizer to remove other impurities. The propylene recovered from the high-pressure propylene is pressurized to 4.3MPa(G) by the propylene feeding pump and sent to the polymerization system;

[0050] (2) Using low-temperature prepolymerization technology, two vertical stirring prepolymerization kettles are operated in parallel. The raw materials include a main catalyst, a co-catalyst, an electron donor and propylene, which enter a vertical prepolymerization kettle with a stirrer for prepolymerization at 30°C and 4MPa(G) for a residence time of 12 minutes; the polymerization reaction heat is withdrawn by means of chilled water introduced into the reactor jacket and the inner cooling pipe; the catalyst and propylene after prepolymerization enter the first reactor for slurry polymerization by means of their own pressure; the slurry polymerization is carried out by two vertical stirred polymerization kettles in parallel, and propylene is slurried in the first reactor at 80°C and 3.6MPa(G) for a residence time of 60 minutes; the polymerization reaction heat is taken away by the vaporization heat of liquid phase propylene and jacket cooling water; the slurry and unreacted propylene in the first reactor enter the third reactor for gas phase polymerization by means of their own pressure under liquid level control; the operating conditions of the third reactor are 80°C, 2.8MPa(G) and a residence time of 45 minutes; the polypropylene powder leaving the third reactor and the carried propylene gas are separated by gas-solid separation, and after the carried propylene gas is separated, a random / copolymerized polypropylene powder; the polypropylene powder coming out of the third reactor enters the fourth reactor, the polymerization temperature of the fourth reactor is 80°C, the polymerization pressure is 2.7MPa(G), and the polypropylene coming out of the fourth reactor is impact-resistant polypropylene; the polypropylene powder coming out of the polymerization system enters the low-pressure filter for gas-solid separation, and the separated propylene gas enters the propylene recovery unit; the separated polypropylene powder enters the steamer to remove the residual propylene, propane and unreacted catalyst, additive and oil, and further reduce the residual VOCs and odor of the polypropylene powder. The temperature of the polypropylene powder leaving the steamer is 105°C, and it is sent to the fluidized bed dryer to remove the residual moisture in the polypropylene powder, and then it is sent to the silo through nitrogen pressurized pneumatic conveying for extrusion granulation packaging. In the exhaust section of the extrusion granulation packaging, at the filter connected to the extruder feed hopper and the mixer flange, the residual VOCs and residual odor in the polypropylene are extracted through a vacuum exhaust device (residual peroxide <5ppm), and the vacuum pump controls the inlet pressure to -10kPa. Ensure the production of polypropylene materials with total carbon volatility less than 50ug(C) / g.

[0051] Comparative Example

[0052] A method for preparing a low VOC polypropylene material comprises the following steps:

[0053] (1) After propylene enters the boundary area of ​​the polypropylene unit, it is roughly dehydrated by the coalescer and then enters the propylene degassing tower to roughly remove light components such as CO and O2. It then passes through the desulfurizer (including organic sulfur hydrolysis and fine desulfurization), silica gel / molecular sieve adsorption dehydration, deoxygenator, and dearsenicizer to remove other impurities. The propylene recovered from the high-pressure propylene is pressurized to 4.3 MPa (G) by the propylene feed pump and sent to the polymerization system;

[0054] (2) Low-temperature prepolymerization process is adopted, and two vertical stirring prepolymerization reactors are operated in parallel. The raw materials including main catalyst, co-catalyst, electron donor and propylene enter the vertical prepolymerization reactor with a stirrer for prepolymerization reaction at 15°C and 3MPa(G), and the residence time is 8min. The heat of polymerization reaction is withdrawn by chilled water introduced into the reactor jacket and internal cooling pipe. The catalyst and propylene after prepolymerization enter the first reactor by their own pressure for slurry polymerization; the slurry polymerization is carried out by two vertical stirred polymerization kettles in parallel, and propylene is slurry polymerized in the first reactor at 65°C and 3.0MPa(G) with a residence time of 40min; the heat of polymerization reaction is taken away by the vaporization heat of liquid propylene and jacket cooling water; the slurry and unreacted propylene in the first reactor enter the third reactor for gas phase polymerization by their own pressure under liquid level control; the operating conditions of the third reactor are 80°C, 2.1MPa(G) and a residence time of 35min; the polypropylene powder leaving the third reactor and the carried propylene gas are separated by gas-solid separation, and after the carried propylene gas is separated, random / copolymerized polypropylene powder is obtained. The polypropylene powder coming out of the polymerization system enters a low-pressure filter for gas-solid separation, and the separated propylene gas enters a propylene recovery unit; the separated polypropylene powder is purged with hot and wet nitrogen to further remove VOCs, and is sent to a fluidized bed dryer to remove residual moisture in the polypropylene powder, and then pneumatically conveyed by nitrogen pressure to a silo for extrusion granulation and packaging. In the exhaust section of the extrusion granulation and packaging, at the filter where the extruder feed hopper and the mixer flange are connected, the residual VOCs and residual odor in the polypropylene are extracted through a vacuum exhaust device, and the vacuum pump controls the inlet pressure to -30 kPa; and the polypropylene material is obtained.

[0055] The melt flow rate was determined according to GB / T 3682-2000 “Determination of mass flow rate and volume flow rate of thermoplastic melts”; the flexural modulus was determined according to GB / T 9341-2008 “Determination of flexural properties of plastics”; the notched impact strength of the simply supported beam was determined according to GB / T 1043.1-2008 “Plastics. Determination of impact properties of simply supported beams. Part 1: Non-instrumented impact test”; the volatile organic compound (VOC) content was determined according to VDA277. The test results are shown in Table 1.

[0056] Table 1 Performance test results of Examples 1-4 and Comparative Examples

[0057]

[0058] The results in Table 1 show that the low-VOC polypropylene material prepared in the example has better processing flowability and mechanical properties, and lower organic volatile content.

[0059] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the contents of the present invention and implement them accordingly. They cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a low VOC polypropylene material, characterized in that: The steps include: Step S1, roughly removing light components CO and O2: After propylene enters the boundary area of ​​the polypropylene device, it is roughly dehydrated in the coalescer and then enters the propylene degassing tower to roughly remove light components CO and O2; Step S2, removing other impurities: the propylene from which the light components CO and O2 are roughly removed in step S1 is sequentially passed through a desulfurizer, a membrane separation dehydrator, a deoxygenator, and a dearsenicizer to remove other impurities; Step S3, polymerization reaction: the propylene from which other impurities have been removed in step S2 and the propylene recovered from the propylene recovery unit are pressurized to a certain pressure by a propylene feeding pump and then fed into a polymerization system, a polymerization reaction is carried out in the polymerization system, and the polypropylene powder discharged from the polymerization system carries the propylene into a low-pressure filter under its own pressure for gas-solid separation, and the separated propylene enters the propylene recovery unit; Step S4, removal of residual VOCs in polypropylene powder: the separated polypropylene powder is introduced into a heater to remove some VOCs in the polypropylene powder at a certain temperature, and then enters a steam evaporator to remove residual propylene, propane and unreacted catalyst, additive and oil, so as to further reduce the residual VOCs and odor of the polypropylene powder; Step S5, dehydration, granulation, and packaging: the polypropylene powder leaving the steamer is sent to a fluidized bed dryer to remove the remaining moisture in the polypropylene powder, and then is conveyed to a silo by nitrogen pressure, and is extruded, granulated, and packaged to obtain a polypropylene material.

2. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The amount of water in the propylene after the crude dehydration in the coalescer in step S1 is ≤3.0×10 -4 wt%.

3. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The desulfurizer in step S2 can perform organic sulfur hydrolysis desulfurization and fine desulfurization; the water content of propylene after dehydration by the membrane separation dehydrator in step S2 is ≤2.0×10 -6 wt%.

4. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The certain pressure in step S3 is 4.3 MPa; the raw materials for the polymerization reaction in step S3 include hydrogen, other olefins and propylene.

5. The method for preparing a low VOC polypropylene material according to claim 4, characterized in that: The other olefin is at least one of ethylene, butene, hexene and octene.

6. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The polymerization system described in step S3 is a production method that adopts a combination of a vertical liquid phase polymerization kettle and a horizontal kettle gas phase polymerization, with a high-efficiency carrier catalyst as the main catalyst, alkyl aluminum as the co-catalyst, silane as the electron donor, hydrogen as the molecular weight regulator, and propylene as the polymerization monomer; polypropylene powder is obtained by prepolymerization, bulk slurry polymerization, and gas phase polymerization.

7. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The polymerization system in step S3 adopts a multi-stage reactor when producing impact-resistant polypropylene, and the third reactor is connected to the fourth reactor through an air lock to control the reaction pressure, temperature, hydrogen concentration of the third reactor and the reactor pressure and temperature of the fourth reactor.

8. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The certain temperature in step S4 is 110-120° C.; the heating method of the heater in step S4 is electric heating or steam heating; the steam of the steamer in step S4 enters the steamer in three ways, passes through a steam distributor, so as to ensure that the polypropylene powder in the steamer is fully in contact with the steam, and removes residual propylene, propane and unreacted catalysts, additives and oil; the polypropylene powder flows in the steamer accompanied by the slow rotation of the stirrer; another low-pressure steam is sent to the steamer heating coil to heat the material inside the steamer, so as to better remove the residue and prevent condensation from forming on the inner wall; under the control of the material level, relying on the action of gravity, the polypropylene powder leaves the steamer from the bottom and enters the fluidized bed dryer.

9. The method for preparing a low VOC polypropylene material according to claim 1, characterized in that: The total carbon volatility of the polypropylene material in step S5 is less than 50ug(C) / g; the fluidized bed dryer in step S5 is a vertical cylindrical structure, the upper part is an expanded structure, and the lower part is a sieve plate type nitrogen distributor; the polypropylene powder enters the fluidized bed dryer from the top, and the hot nitrogen circulates in the nitrogen closed loop and enters the fluidized bed dryer through the sieve plate distributor; Nitrogen and polypropylene powder are in countercurrent contact; the spiral plate in the fluidized bed dryer causes the powder to move in a piston flow and removes moisture from the polypropylene powder at the same time; the exhaust section of the extrusion granulation packaging in step S5 is at the filter connected to the flange of the extruder feed hopper and the mixer, and the residual VOCs and residual odor in the polypropylene are extracted through a vacuum exhaust device, and the vacuum pump controls the inlet pressure to be -30 to -10 kPa.

10. A low-VOC polypropylene material made by the method for preparing a low-VOC polypropylene material according to any one of claims 1 to 9.

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