Continuous suspension process polypropylene grafting modification system and method

Abstract

This invention relates to the field of polymer grafting technology, and discloses a system and method for continuous suspension grafting of monomers onto polypropylene. The system includes a grafting reactor, a particle dryer, and a devolatilizer. The grafting reactor is used to carry out the grafting reaction; the particle dryer is used to perform solid-liquid separation to obtain a solid product and a liquid medium; the devolatilizer is used to perform devolatilization treatment on the solid product obtained from the solid-liquid separation. The grafting reactor is equipped with a submerged pipe and an overflow port at the top. The submerged pipe allows materials from the raw material premixing device to continuously enter the underwater portion of the grafting reactor, and the overflow port is used to continuously extract the grafting reaction products. Using the equipment and method of this invention, not only can continuous suspension grafting of monomers onto polypropylene be achieved, but also grafted products with high grafting rates can be obtained.

Description

Technical Field

[0001] This invention relates to the field of polymer grafting technology, and more specifically to a system and method for continuous suspension method of polypropylene grafting modification. Background Technology

[0002] Polypropylene, a general-purpose plastic, is widely used in various fields such as home furnishings, appliances, automobiles, and packaging. However, due to the lack of polar functional groups, polypropylene exhibits poor dyeability, low-temperature toughness, adhesion, antistatic properties, and hydrophilicity, and its compatibility with reinforcing materials and inorganic fillers is also unsatisfactory. To expand the application range of polypropylene, it needs to be modified, such as through grafting, blending, filling, and composite reinforcement modification. Among these, grafting modification has been widely applied and has achieved good results in the fields of polypropylene blending with nylon and glass fiber and inorganic particle-filled polypropylene.

[0003] Common grafting methods include solution grafting, melt grafting, solid-phase grafting, and suspension grafting. Suspension grafting, in particular, adds water or an aqueous solution to solid-phase grafting to improve uneven heating and prevent sticking to the reactor in polypropylene. Currently, the most mature polar monomer grafted products on the market are maleic anhydride-grafted polypropylene products obtained through melt grafting, with several large international companies offering related products, such as ExxonMobil. Montell's Hivalloy process utilizes spherical "reactor particle" technology to introduce non-olefinic monomers into polypropylene particles. They launched the Hivalloy PP-PS alloy, which combines the advantages of PP (low price, light weight, and chemical resistance) with the high rigidity of PS.

[0004] US5585435 discloses a continuous solid-phase grafting method for fluidizing polypropylene powder using steam / alcohol vapor and adding a vaporized monomer initiator. CN1704436A discloses an improved reactor with internal and external double spiral ribbons, which can realize continuous solid-phase grafting of powder. Currently, there are no reports on continuous suspension grafting production processes for polypropylene. Summary of the Invention

[0005] The purpose of this invention is to overcome the fact that there is no existing system that can achieve continuous suspension grafting of monomers onto polypropylene. Therefore, this invention provides a system and method for continuous suspension grafting modification of polypropylene.

[0006] To achieve the above objectives, the first aspect of the present invention provides a system for continuous suspension polypropylene grafting modification, the system comprising a grafting reactor, a particle dryer, and a devolatilizer;

[0007] The grafting reactor is used to carry out the grafting reaction;

[0008] The particle dryer is used to perform solid-liquid separation to obtain solid products and liquid media.

[0009] The devolatilizer is used to perform devolatilization treatment on the solid phase product obtained by solid-liquid separation.

[0010] The grafting reactor is equipped with a submerged pipe and an overflow port at the top. The submerged pipe is used to continuously allow the material in the raw material premixing device to enter the underwater portion of the grafting reactor, and the overflow port is used to continuously extract the products of the grafting reaction.

[0011] A second aspect of the present invention provides a method for continuous suspension grafting of monomers onto polypropylene, the method comprising: continuously adding a premix containing a swelling monomer, an initiator and polypropylene powder to water for a grafting reaction; continuously extracting the grafting reaction product and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of monomers.

[0012] Preferably, the method is implemented in the system described in the first aspect.

[0013] The equipment and method of this invention can not only realize the continuous suspension grafting of polypropylene monomers, especially suitable for grafting monomers that have a swelling effect on polypropylene, but also can be used to prepare products with a high grafting rate. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the production process of polypropylene continuous suspension grafting swelling monomer according to one embodiment of the present invention.

[0015] Figure 2 This is an infrared comparison analysis diagram of the grafted product and polypropylene in Embodiment 1 of the present invention.

[0016] Explanation of reference numerals in the attached figures

[0017] 1-Raw material mixing vessel 2.1-First swelling reaction vessel

[0018] 3-Demineralized water tank 4-Grafting reactor

[0019] 5-Particle dryer 6-Devolve unit

[0020] 7-Heat exchanger 8-Circulating fan

[0021] 9-Heater 10-Circulating water pump

[0022] 12-Induced draft fan 2.2-Second swelling reactor Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The first aspect of this invention provides a continuous suspension method for polypropylene grafting modification, the system comprising a grafting reactor, a particle dryer, and a devolatilizer;

[0025] The grafting reactor is used to carry out the grafting reaction;

[0026] The particle dryer is used to perform solid-liquid separation to obtain solid products and liquid media.

[0027] The devolatilizer is used to perform devolatilization treatment on the solid phase product obtained by solid-liquid separation.

[0028] The grafting reactor is equipped with a submerged pipe and an overflow port at the top. The submerged pipe is used to continuously allow the material in the raw material premixing device to enter the underwater portion of the grafting reactor, and the overflow port is used to continuously extract the products of the grafting reaction.

[0029] According to the present invention, preferably, the grafting reactor is equipped with a stirrer suitable for solid-liquid mixing systems, including but not limited to three- or four-bladed turbine impellers, ribbon stirrers, and single- or multi-layer three- or four-bladed inclined impellers. The grafting reactor may also be equipped with two or more baffles to enhance the uniform dispersion of solid particles in water. The grafting reactor should have at least two feed inlets, respectively connected to a submerged pipe and a demineralized water tank. Material from the raw material premixing device enters the lower part of the grafting reactor under pressure through the submerged pipe, ensuring the mixing of the newly added material with the original material in the reactor. The overflow port at the top of the grafting reactor is connected to a particle dryer, allowing the grafting reaction product to enter the particle dryer through the overflow port.

[0030] According to the present invention, preferably, the length of the submersible tube is such that the distance between the port of the submersible tube on the water-immersed side and the water surface is not less than 5 cm, and preferably 8-15 cm.

[0031] According to the present invention, preferably, the system further includes a demineralized water tank for continuously supplying water to the grafting reactor.

[0032] According to the present invention, preferably, the demineralized water tank is connected to the particle dryer, so that the liquid phase medium separated by the particle dryer flows into the demineralized water tank for reuse. A filtration device may also be provided between the particle dryer and the demineralized water tank, so that the liquid phase medium separated by the particle dryer is filtered before flowing into the demineralized water tank.

[0033] According to the present invention, preferably, the demineralized water tank is equipped with a stirrer and a jacket. The stirrer is used to mix the original water in the demineralized water tank, the newly added water, and the recycled water separated by the particle dryer. The jacket is used to regulate the feed water temperature by introducing low-pressure steam or circulating water according to process requirements. More preferably, the temperature of the water in the demineralized water tank is the same as the temperature of the grafting reaction.

[0034] According to the present invention, preferably, the particle dryer is equipped with an induced draft fan, which provides an air source for the particle dryer. The induced draft fan and the particle dryer work together to perform solid-liquid separation to obtain a solid product and a liquid medium.

[0035] According to the present invention, the particle dryer is used for solid-liquid separation to obtain a solid product and a liquid medium; the liquid medium is recycled to a demineralized water tank via a circulating water pump, the pump being equipped with a pre-pump filter to prevent polypropylene powder or grafted monomer oligomer insoluble solids from entering the circulating water pump and causing blockage. More preferably, a portion of the liquid medium after filtration is used as recycled water, and the remainder is discharged as wastewater. More preferably, the weight flow ratio of the recycled water to the wastewater is 1:5-10, more preferably 1:7-8.

[0036] According to the present invention, preferably, the system further includes a heat exchanger, a circulating fan, and a heater connected in sequence, wherein the heat exchanger and the heater are respectively connected to the top and bottom of the devolatilizer. The heat exchanger, circulating fan, and heater are auxiliary equipment of the devolatilizer, and the devolatilizer, together with the heat exchanger, circulating fan, heater, and devolatilizer, complete the devolatilization treatment of solid products.

[0037] Moisture and residual volatile components in the polypropylene graft are vaporized in the devolatilizer and then condensed and discharged after condensation. The dried graft can be packaged directly or mixed with other components for granulation.

[0038] In this invention, the reaction raw materials are accurately measured, and corresponding metering devices should be provided, including but not limited to metering pumps, metering tanks, and loss-in-weight balances. Specific setup methods are well known to those skilled in the art and will not be described in detail here.

[0039] According to the present invention, preferably, the system further includes a raw material premixing device, which is a continuous conveying mixer used to premix the initiator, graft monomer and polypropylene powder.

[0040] According to the present invention, preferably, the continuous conveying mixer should be supplied with a small flow of nitrogen to maintain a slight positive pressure inside and ensure the pressure at the outlet. More preferably, the pressure is not less than 0.2 bar, and more preferably 0.3-0.5 bar.

[0041] According to the present invention, preferably, the system further includes a raw material premixing device, which includes a raw material mixing vessel and a swelling reaction vessel. The raw material mixing vessel is used to premix the initiator and the grafted monomer, and the swelling reaction vessel is used to mix the premixed product with polypropylene powder to carry out a swelling reaction. The grafted monomer is a swelling monomer.

[0042] According to the present invention, preferably, after the reaction in the swelling reactor is completed, a small flow rate of nitrogen should be introduced into the swelling reactor to ensure the conveying of the swollen material. More preferably, the pressure is not less than 0.2 bar, and more preferably 0.3-0.5 bar.

[0043] According to the present invention, preferably, the function of the raw material mixing vessel is to mix the solid material (initiator) and the liquid material (swellable monomer) evenly. The raw material mixing vessel is equipped with a stirrer and a jacket. Circulating water can be circulated in the jacket to maintain the vessel temperature below 40°C, preferably 10-30°C, to prevent the monomer from undergoing a polymerization reaction.

[0044] According to the present invention, preferably, the swelling reactor includes at least two swelling reactors connected in parallel, which work alternately to ensure the material supply to the grafting reactor.

[0045] A second aspect of the present invention provides a method for continuous suspension grafting of monomers onto polypropylene, the method comprising: continuously adding a premix containing a swelling monomer, an initiator and polypropylene powder to water for a grafting reaction; continuously extracting the grafting reaction product and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of monomers.

[0046] According to the present invention, preferably, the method is implemented in the system described in the first aspect.

[0047] According to the present invention, preferably, the amount of the swelling monomer is 1-25 parts by weight, more preferably 2-18 parts by weight, and more preferably 10-18 parts by weight, relative to 100 parts by weight of polypropylene powder, and the amount of the initiator is 0.01-0.6 parts by weight.

[0048] According to the present invention, preferably, the method further includes premixing the swellable monomer and the initiator, then subjecting the premixed product to a swelling reaction with polypropylene powder, followed by a grafting reaction. The conditions for premixing the swellable monomer and the initiator are not particularly limited, as long as the initiator is uniformly dispersed in the swellable monomer. The inventors of this invention have discovered that when a non-swellable monomer is used instead of the swellable monomer, and the amount of the non-swellable monomer is large, the non-swellable monomer and polypropylene powder in the swelling reactor become sticky, preventing normal delivery to the grafting reactor and causing the reaction to stop. This indicates that the apparatus of the present invention is not suitable when the amount of non-swellable monomer is large.

[0049] According to the present invention, preferably, the swelling reaction is carried out at a temperature of 35-65°C, more preferably at 40-45°C, for a time of 1-6 hours, more preferably 2-5 hours.

[0050] According to the present invention, preferably, the weight flow ratio of the polypropylene powder to water is 1:2-8.

[0051] According to the present invention, preferably, the temperature of the grafting reaction is 80-95°C, more preferably 85-92°C, and the time is 2-10h, more preferably 3-8h.

[0052] According to the present invention, preferably, the devolatilization treatment is performed at a temperature of 100-120°C for a time of 0.5-1 hour. During the devolatilization treatment, not only are moisture and volatiles removed from the grafted product, but the residual initiator in the grafted product is also further decomposed and deactivated, thereby improving the performance of the grafted product.

[0053] According to the present invention, preferably, the initiator is a peroxide-based free radical initiator with a half-life of less than 90 min at 90°C; more preferably, the initiator is at least one selected from benzoyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide (2-ethylhexanoate), and dicyclohexyl peroxide.

[0054] According to the present invention, preferably, the swelling monomer is a liquid-phase monomer containing unsaturated double bonds and functional groups that has a swelling effect on polypropylene powder; more preferably, the swelling monomer includes a first swelling monomer and an optional second swelling monomer, wherein the first swelling monomer is a C5-C12 hydrocarbon containing unsaturated bonds, and the second swelling monomer is an acrylate and / or a C3-C7 organic compound containing anhydride groups. The swelling monomer can diffuse into the interior of the polypropylene powder, and compared with non-swellable monomers, the fully swollen polypropylene powder can still maintain good flowability even under high addition conditions.

[0055] According to the present invention, preferably, the first swelling monomer is at least one of styrene, α-methylstyrene and vinylpyridine.

[0056] According to the present invention, preferably, the C3-C7 organic compound containing anhydride groups is maleic anhydride.

[0057] According to the present invention, preferably, the weight ratio of the second swollen monomer to the first swollen monomer is 1:2-8.

[0058] According to the present invention, the polypropylene powder can be a powder obtained by reactor particle technology using a Ziegler-Natta catalyst, without any melt granulation or addition of antioxidants. Preferably, the polypropylene powder is homopolymer polypropylene and / or random copolymer polypropylene; or, the polypropylene powder is impact-resistant polypropylene. More preferably, the particle size distribution of the polypropylene powder is between 0.2-3 mm, preferably 0.5-3 mm. The random copolymer polypropylene uses ethylene and / or α-olefin as comonomers, wherein the α-olefin is one of butene, hexene, or octene. For example, the random copolymer polypropylene can be ethylene-propylene copolymer impact-resistant polypropylene powder. The xylene-soluble content in the polypropylene powder is 1-70 wt%, preferably 1.5-65 wt%. The xylene-soluble content in the polypropylene powder is tested according to the method of GB / T24282-2009 (Determination of xylene-soluble content in polypropylene plastics).

[0059] Combination Figure 1 The method for continuous suspension grafting of polypropylene monomers according to the present invention is described in which the swelling monomer and the initiator are metered and added to the raw material mixing vessel 1 for a second mixing, and then the second mixture product and the polypropylene powder metered in proportion are fed into the first swelling reactor 2.1 or the second swelling reactor 2.2 for swelling at a set temperature. The swollen material is continuously fed into the grafting reactor 4 through a submersible pipe under nitrogen pressure. At the same time, water from the demineralized water tank 3 is continuously fed into the grafting reactor 4 through another inlet. The swollen monomer, initiator and polypropylene powder undergo a grafting reaction underwater in the grafting reactor 4. The slurry from the grafting reaction is continuously drawn out through the overflow port at the top of the grafting reactor 4 and enters the granule dryer 5. The slurry from the grafting reaction undergoes solid-liquid separation in the granule dryer 5 to obtain a liquid medium and a solid product. After being filtered by a filter, part of the liquid medium is returned to the demineralized water tank 3 as recycled water via the circulating water pump 10, and the remainder is discharged as wastewater. The solid product enters the devolatilizer 6. Under the combined action of the heat exchanger 7, the circulating fan 8, the heater 9 and the devolatilizer 6, the devolatilization treatment of the solid product is completed to obtain the product.

[0060] The present invention will be described in detail below through embodiments. In the following embodiments,

[0061] Grafting rate test method: Place 2-4g of grafted product into a Soxhlet extractor and extract with acetone for 24 hours to remove unreacted monomers and their homopolymers, and obtain pure grafted product. Dry and weigh the product, and calculate the grafting rate (Gp%) = (W1-W0) / W0×100%; where W1 is the weight of grafted polypropylene and W0 is the weight of ungrafted polypropylene.

[0062] Infrared characterization of grafted groups: 2-4g of grafted product was placed in a Soxhlet extractor and extracted with acetone for 24 hours to remove unreacted monomers and their homopolymers, resulting in pure grafted product. The product was then hot-pressed into thin sheets, and the characteristic peaks of functional groups on the grafted modified polypropylene could be observed by quantitative Fourier transform infrared (FTIR) spectroscopy.

[0063] Polypropylene A: Granular homopolymer polypropylene powder with a particle size distribution between 0.5-2 mm. The content of xylene-soluble substances in the polypropylene powder is 2.3 wt%.

[0064] Polypropylene B: Granular ethylene-propylene copolymer impact-resistant polypropylene powder with a particle size distribution between 1-3 mm. The content of xylene-soluble substances in the polypropylene powder is 47.8 wt%.

[0065] Example

[0066] The swelling monomer and initiator are metered and added to the raw material mixing vessel 1 for mixing. The mixed product and polypropylene powder measured according to the ratio are then sent to the first swelling reactor 2.1 or the second swelling reactor 2.2 for swelling at a set temperature. The swollen material is continuously introduced into the lower part of the grafting reactor 4, which has been pre-stored with deionized water, through a submerged pipe (located 10 cm below the liquid surface) under nitrogen pressure (0.3 bar). The outlet of the submerged pipe is located below the water level. At the same time, water from the demineralized water tank 3 continuously enters the grafting reactor 4 through another inlet. This allows the swollen monomer, initiator, and polypropylene powder to undergo a grafting reaction underwater in the grafting reactor 4. The slurry from the grafting reaction is continuously drawn out through the overflow port at the top of the grafting reactor 4 and then enters the granule dryer 5. The slurry from the grafting reaction undergoes solid-liquid separation in the granule dryer 5 to obtain a liquid medium and a solid product. After being filtered by a filter, part of the liquid medium is returned to the demineralized water tank 3 as recycled water via the circulating water pump 10, and the remainder is discharged as wastewater. The solid product enters the devolatilizer 6 to remove volatiles. Under the combined action of the heat exchanger 7, the circulating fan 8, the heater 9, and the devolatilizer 6, the devolatilization treatment of the solid product is completed to obtain the final product. The specific reaction conditions and product properties of Examples 1-5 are shown in Table 1.

[0067] Figure 2 This is an infrared comparison analysis image of the grafted product and polypropylene powder from Example 1. The image shows that the grafted product... (The sentence is incomplete and requires further context to translate accurately.) -1 The presence of a bimodal characteristic peak nearby indicates that styrene has been grafted onto the polypropylene powder.

[0068] Table 1

[0069]

[0070] Example 6

[0071] The grafting reaction was carried out according to the method of Example 1, except that the depth of the submerged tube below the liquid surface was 6 cm. The yield was 32.3 kg / h, and the grafting rate was 4.5%.

[0072] Example 7

[0073] The grafting reaction was carried out according to the method of Example 1, except that the grafting monomer, initiator, and polypropylene powder were mixed and directly fed into the grafting reactor through a submersible pipe, meaning the grafting monomer did not undergo a swelling process. The yield was 31.9 kg / h, and the grafting rate was 3.1%.

[0074] Comparative Example 1

[0075] The grafting reaction was carried out according to the method of Example 1, except that the swollen material was not fed into the grafting reactor directly through the inlet without passing through the submersible tube. The yield was 31.6 kg / h, and the grafting rate was 2.6%.

[0076] The equipment and method of this invention can not only achieve continuous suspension grafting of monomers onto polypropylene, but are also applicable to the preparation of polypropylene graft copolymers with high grafting rates. As shown in Examples 1-7, using the method of this invention, the yield of grafted products is 31-60 kg / h, and the grafting rate is 2-9 wt%. Particularly preferably, using the method of Examples 1-2, the yield of grafted products is 33-52 kg / h, and the grafting rate is 5.6-8.7 wt%.

[0077] A comparison of Examples 1 and 7 shows that omitting the swelling step results in insufficient diffusion of the monomer in polypropylene, which leads to a significant decrease in yield and product grafting rate.

[0078] By comparing Example 1 with Comparative Example 1, it can be seen that without using submersible feeding, the yield and product grafting rate are significantly reduced.

[0079] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A continuous suspension method for polypropylene grafting modification, characterized in that, The system includes a raw material premixing unit, a grafting reactor, a particle dryer, and a devolatilizer; The raw material premixing device includes a raw material mixing vessel and a swelling reaction vessel. The raw material mixing vessel is used to premix the initiator and the grafted monomer, and the swelling reaction vessel is used to mix the premixed product with polypropylene powder to carry out a swelling reaction. The grafting reactor is used to carry out the grafting reaction; The particle dryer is used to perform solid-liquid separation to obtain solid products and liquid media. The devolatilizer is used to perform devolatilization treatment on the solid product obtained from solid-liquid separation; the devolatilization treatment temperature is 100-120℃ and the time is 0.5-1h; The swelling reactor comprises at least two parallel swelling reactors, which operate alternately to ensure the material supply to the grafting reactor. The grafting monomer is a swelling monomer, which includes a first swelling monomer and an optional second swelling monomer. The first swelling monomer is at least one of styrene, α-methylstyrene, and vinylpyridine. The second swelling monomer is an acrylate and / or a C3-C7 organic compound containing an anhydride group. After the reaction in the swelling reactor is completed, a small flow of nitrogen is introduced into the swelling reactor to ensure the transport of the swollen material. The amount of the swelling monomer is 1-25 parts by weight relative to 100 parts by weight of polypropylene powder, and the amount of the initiator is 0.01-0.6 parts by weight. The particle size distribution of polypropylene powder is between 0.2 and 3 mm; The grafting reactor is equipped with a submerged pipe and an overflow port at the top. The submerged pipe is used to continuously allow the material in the raw material premixing device to enter the underwater portion of the grafting reactor, and the overflow port is used to continuously draw out the products of the grafting reaction. The weight flow ratio of the polypropylene powder to water is 1:2-8. The temperature of the grafting reaction is 80-95℃, and the time is 2-10 h. The length of the submersible tube is such that the distance between the end of the submersible tube immersed in water and the water surface is 8-15cm.

2. The system according to claim 1, wherein, The system also includes a demineralized water tank for continuously supplying water to the grafting reactor.

3. The system according to claim 2, wherein, The demineralized water tank is connected to the particle dryer, so that the liquid medium separated by the particle dryer flows into the demineralized water tank for reuse.

4. The system according to claim 1, wherein, The system also includes a heat exchanger, a circulating fan, and a heater connected in sequence, with the heat exchanger and heater respectively connected to the top and bottom of the devolatilizer.

5. A method for continuous suspension grafting of monomers onto polypropylene, characterized in that, The method includes: continuously adding a premix containing a swelling monomer, an initiator, and polypropylene powder underwater to carry out a grafting reaction; continuously extracting the grafting reaction product and adding water to maintain the water content in the grafting reaction system, thereby achieving continuous grafting of monomers; the method is implemented in the system described in any one of claims 1-4.

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