Method for removing impurities in polyolefin organic solution

Abstract

The invention provides a method for removing impurities in a polyolefin organic solution, and belongs to the technical field of polyolefin production processes. The method comprises the following steps: directly contacting polyacrylamide with a polyolefin organic solution, so that impurities in the polyolefin organic solution are removed through adsorption complexation or adsorption bridging of polyacrylamide; and separating the polyolefin organic solution from which the impurities are removed from polyacrylamide to obtain a purified polyolefin organic solution.

Description

Technical Field

[0001] The invention relates to the technical field of polyolefin production technology, in particular to a method for removing impurities from a polyolefin organic solution. Background Art

[0002] Polyolefin elastomer is an important material with high transparency, excellent dimensional stability, good compatibility and affinity with polyolefin substrates. It is widely used in the manufacture of automotive parts, insulation and protection of wires and cables, design and production of mechanical tools, development of footwear materials, construction of high-performance seals, preparation of adhesive materials such as hot melt adhesives. However, when the catalyst is destroyed during the production process, ligands will be separated. These ligands are dissolved in the product and have strong color rendering, which has a great impact on the transparency and color of the final product.

[0003] In the production process of polyolefin elastomers, impurities are usually removed by flash evaporation. In the process of preparing polyolefin elastomers by diimine nickel catalysis, due to the fluctuations in temperature and pressure in the reactor, some olefin monomers may not react completely and remain in the polyolefin organic solution. During the solution polymerization process, the polyolefin elastomer will be completely dissolved in the reaction solvent, making it combined with the polyolefin elastomer chain segment, which is difficult to remove by physical methods. At the same time, the stability and temperature resistance of diimine nickel catalysts are relatively high, which means that conventional physical methods such as flash evaporation and filtration are difficult to remove impurities such as unreacted catalysts and ligands from polyolefin organic solutions. Summary of the invention

[0004] In view of this, in order to at least partially solve at least one of the above-mentioned technical problems, the present invention provides a method for removing impurities from a polyolefin organic solution.

[0005] According to an embodiment of one aspect of the present invention, a method for removing impurities from a polyolefin organic solution is provided, comprising: directly contacting polyacrylamide with the polyolefin organic solution so that the impurities in the polyolefin organic solution are removed by adsorption complexation or adsorption bridging of the polyacrylamide; separating the polyolefin organic solution after the impurities are removed from the polyacrylamide to obtain a purified polyolefin organic solution.

[0006] According to an embodiment of the present invention, the polyacrylamide includes at least one of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide.

[0007] According to an embodiment of the present invention, the molecular weight of polyacrylamide is 10 to 30 million.

[0008] According to an embodiment of the present invention, direct contact includes preparing polyacrylamide into an aqueous solution, contacting it with the polyolefin organic solution through water washing; or preparing a packed column using polyacrylamide as a filler, and contacting it with the polyolefin organic solution through the packed column.

[0009] According to an embodiment of the present invention, contacting the polyolefin organic solution by water washing includes: passing the aqueous solution of polyacrylamide into the polyolefin organic solution and stirring and mixing, so as to perform a direct contact operation.

[0010] According to an embodiment of the present invention, when the aqueous solution of polyacrylamide is introduced into the polyolefin organic solution and stirred and mixed, the stirring and mixing temperature is 80-120° C., and the stirring and mixing time is 5-30 min; the introduction rate of the aqueous solution of polyacrylamide is 10-100 mL / min; the volume ratio of the polyolefin organic solution to the aqueous solution of polyacrylamide is (5-15):1; and the mass fraction of polyacrylamide in the aqueous solution of polyacrylamide is 0.01-5%.

[0011] According to an embodiment of the present invention, when polyacrylamide is used as a filler to prepare a packed column, the separation includes: passing the polyolefin organic solution through a solid column filled with polyacrylamide and then flowing out to obtain a purified polyolefin organic solution.

[0012] According to an embodiment of the present invention, the volume of polyacrylamide in the solid column filled with polyacrylamide is 60-95% of the volume of the solid column; the solid column is also filled with ceramic balls, and the particle size of the ceramic balls is 3-5mm; the volume of the ceramic balls is 5-40% of the volume of the solid column; the upper and lower ends of the solid column also respectively include filling layers of ceramic balls.

[0013] According to an embodiment of the present invention, when the polyolefin organic solution passes through a solid column filled with polyacrylamide, the temperature is 80-120° C., the temperature is kept for 10-60 minutes, and the pressure is 0.1-1 MPa.

[0014] According to an embodiment of the present invention, a polyolefin organic solution is prepared by the following method: a comonomer, a main catalyst and a co-catalyst are added to an organic solvent to carry out a polymerization reaction to obtain a polyolefin organic solution; the organic solvent comprises one or more of n-hexane, isobutane, isopentane, n-heptane, n-octane, isooctane, toluene and dichloromethane; the comonomer comprises ethylene; the main catalyst comprises an α-diimine nickel catalyst; the co-catalyst comprises one or more of diethylaluminum chloride and triethylaluminum chloride; the polymerization reaction temperature is 35-80°C, the polymerization reaction time is 20-60min, and the polymerization reaction pressure is 0.5-5MPa.

[0015] According to an embodiment of the present invention, the polyolefin is a polyolefin elastomer, the polyolefin organic solution is a polyolefin glue, and the impurities include ligands decomposed by the main catalyst during the reaction, unreacted main catalyst and unreacted co-catalyst, wherein the ligands are, for example, acenaphthenequinone decomposed by the main catalyst, bromobenzene separated from the main catalyst, etc. The above-mentioned ligands appear dark yellow in the polyolefin glue and have a certain influence on the transmittance of visible light and ultraviolet light.

[0016] According to an embodiment of the present invention, the method for removing impurities in a polyolefin organic solution provided by the present invention directly contacts polyacrylamide with a polyolefin organic solution, and the long-chain structure of polyacrylamide provides a large number of contact sites, which helps to enhance the interaction between it and impurities and enhance adsorption capacity. Polyacrylamide has an amide group, which interacts with polar molecules to form hydrogen bonds, so that polyacrylamide can be closely adsorbed on the surface of these substances containing hydrogen bond receptors, forming adsorption complexation, and increasing the stability of adsorption. In particular, polyolefin organic solutions usually contain particles or molecules with a relatively large amount of hydrogen bond receptors, which, by means of the long-chain structure of polyacrylamide, help to form hydrogen bond interactions with multiple particles or molecules, thereby connecting multiple particles or molecules to form flocs or coacervates, forming adsorption bridging, and realizing the removal of impurities in polyolefin organic solutions, such as the removal of the chromogenic ligand separated by the main catalyst. The polyolefin elastomer prepared by the subsequent steps of the polyolefin organic solution after the removal of impurities is colorless and transparent, has good ultraviolet and visible light transmittance, and reduces the yellowness index of the polyolefin elastomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The flowchart of the method for removing impurities from a polyolefin organic solution of the present invention is shown.

[0018] In the drawings, the meanings of the reference numerals are as follows:

[0019] S101-first operation;

[0020] S102-second operation. DETAILED DESCRIPTION

[0021] Below, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of embodiments of the present invention. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of concepts of the present invention.

[0022] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. The term "comprising" used herein indicates the existence of features, steps, operations, but does not exclude the existence or addition of one or more other features.

[0023] In the case of using expressions such as "at least one of A, B, and C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.). In the case of using expressions such as "at least one of A, B, or C, etc.", it should generally be interpreted in accordance with the meaning of the expression generally understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0024] Polyolefin elastomers, as a polymer prepared by coordination polymerization mediated by metallocene catalysts, are usually elastic materials obtained by copolymerization of ethylene and α-olefin monomers (such as 1-butene, 1-hexene or 1-octene), showing a series of excellent physical and chemical properties. In view of its multifunctional performance advantages, polyolefin elastomers have been widely used in many industrial fields. In the preparation process of polyolefin elastomers, due to the fluctuations of temperature and pressure in the reactor, some impurities such as unreacted monomers, catalysts, and reaction by-products still exist in the polyolefin organic solution after the polymerization reaction. Therefore, it is necessary to remove impurities in the polyolefin organic solution before preparing polyolefin elastomers.

[0025] Due to the high viscosity of polyolefin organic solutions, impurities such as incompletely reacted catalysts and ligands formed by catalyst decomposition are usually easily tightly combined with the target product polyolefin elastomer and are difficult to remove by conventional physical methods such as flash evaporation and filtration.

[0026] In the process of realizing the concept of the present invention, it was found that with the help of the amide group in polyacrylamide, it is possible to form an adsorption complex or adsorption bridge with particles or molecules having hydrogen bond acceptors in the polyolefin organic solution, such as particles or molecules containing polar groups (catalysts used in the preparation of polyolefin organic solutions, additives commonly used in polymerization reactions, plasticizers, etc.), so that impurities in such particles or molecules are separated from the polyolefin organic solution along with the polyacrylamide, thereby achieving purification of the polyolefin organic solution.

[0027] Specifically, according to an embodiment of one aspect of the present invention, a method for removing impurities from a polyolefin organic solution is provided. Figure 1 A flow chart of a method for removing impurities from a polyolefin organic solution of the present invention is shown, and the method includes operations S101 to S102.

[0028] In the first operation S101, polyacrylamide is directly contacted with a polyolefin organic solution, so that impurities in the polyolefin organic solution are removed through adsorption complexation or adsorption bridging of the polyacrylamide.

[0029] According to the embodiment of the present invention, polyacrylamide is a linear polymer with a relatively high molecular weight, and contains a large number of amide groups (-CONH2) in its molecular weight. The amide groups are polar and hydrophilic, and can form hydrogen bond interactions with polar groups in impurities, thereby adsorbing impurities, such as unreacted catalysts and ligands formed by catalyst decomposition, onto the molecular chain of polyacrylamide. The long chain structure of polyacrylamide can also adsorb impurity molecules through physical effects such as van der Waals forces. The long chain structure of polyacrylamide enables it to stretch in a polyolefin organic solution, adsorb multiple impurity particles at the same time, connect multiple particles together, form larger flocs or aggregates, and form an adsorption bridging effect. The flocs or aggregates formed by the adsorption bridging effect can be easily precipitated or filtered out from the polyolefin organic solution.

[0030] In the second operation S102, the polyolefin organic solution after impurities are removed is separated from the polyacrylamide to obtain a purified polyolefin organic solution.

[0031] According to the embodiment of the present invention, after the previous operation, polyacrylamide has formed an adsorption complex with impurities in the polyolefin organic solution or formed larger flocs through bridging. These flocs contain a large amount of impurities, thereby greatly reducing the concentration of impurities in the solution, and then separation is more convenient than conventional flash evaporation without adsorbent treatment. The separation means can be, for example, sedimentation, centrifugal separation or filtration as needed.

[0032] According to the embodiments of the present invention, by directly contacting polyacrylamide with a polyolefin organic solution, hydrogen bonding interactions are formed between the particles or molecules with polarity, and adsorption complexation is formed to connect them to form an adsorption bridging effect, which helps to remove impurities. Since impurities in the polyolefin organic solution are removed more thoroughly, the prepared polyolefin elastomer has higher performance.

[0033] According to an embodiment of the present invention, the polyolefin organic solution is prepared by the following method:

[0034] Adding comonomer, main catalyst and cocatalyst into an organic solvent to carry out polymerization reaction to obtain a polyolefin organic solution; the organic solvent includes: one or more of n-hexane, isobutane, isopentane, n-heptane, n-octane, isooctane, toluene and dichloromethane; preferably n-hexane and n-heptane, more preferably n-heptane. The comonomer includes ethylene; the main catalyst includes α-diimine nickel catalyst; the cocatalyst includes one or more of diethylaluminum chloride and triethylaluminum chloride; the polymerization reaction temperature is 35-80°C, the polymerization reaction time is 20-60min, and the polymerization reaction pressure is 0.5-5MPa.

[0035] In one specific embodiment, the polyolefin organic solution of the present invention uses ethylene as a comonomer and is polymerized under the catalytic action of an α-diimine nickel catalyst and a cocatalyst. After the polymerization reaction is completed, the polyolefin organic solution includes the target polyolefin elastomer, the α-diimine nickel catalyst used for the polymerization reaction, the cocatalyst, the unreacted comonomer, the reaction by-products and other impurities.

[0036] Specifically, the polyolefin is a polyolefin elastomer, such as vinyl polyolefin elastomer (EPOE). The polyolefin organic solution is a polyolefin glue, and the impurities include ligands decomposed by the main catalyst during the reaction, unreacted main catalyst and unreacted co-catalyst, and the main catalyst can be, for example, a metallocene catalyst, an α-diimine nickel catalyst, etc. Among them, the ligands include acenaphthenequinone decomposed by the main catalyst, bromobenzene separated from the main catalyst, etc., and the above ligands appear dark yellow in the polyolefin glue, as well as impurities caused by environmental pollution or the raw materials themselves during the production process.

[0037] According to an embodiment of the present invention, polyacrylamide includes at least one of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide, preferably includes at least one of anionic polyacrylamide and cationic polyacrylamide. The molecular weight of polyacrylamide is 10 to 30 million, for example, it can be 100,000, 500,000, 700,000, 1 million, 10 million, 15 million, 20 million, 24 million, 26 million or 30 million. In the process of performing the relevant experiments of the present invention, it is found that when the above-mentioned types of polyacrylamide are used and the molecular weight is adjusted within the above range, the removal effect of impurities such as unreacted catalysts and ligands is better, and the light transmittance and volume resistivity of the prepared polyolefin elastomer are higher.

[0038] Specifically, when using cationic polyacrylamide, since its molecular chain carries positively charged groups, these positive charges will attract negatively charged impurity particles in aqueous solution. Impurities such as negatively charged particles and organic matter in polyolefin organic solution, such as the main catalyst, co-catalyst, olefin monomer, etc. that may be used in the polymerization process of polyolefin elastomers, are adsorbed by cationic polyacrylamide to its surroundings through electrostatic attraction, so that the surface charge of the particles is neutralized, thereby reducing the electrostatic repulsion between particles, and further promoting the aggregation and sedimentation of impurity particles such as catalysts and ligands that have not reacted completely on the basis of adsorption complexation or adsorption bridging.

[0039] Preferably, the molecular weight of the cationic polyacrylamide is 700,000.

[0040] Specifically, when anionic polyacrylamide is used, it exhibits the characteristics of a polymer electrolyte in a neutral or alkaline solution. The negatively charged groups on the molecular chain of anionic polyacrylamide can generate electrostatic attraction with positively charged ions or particles in the polyolefin organic solution. Although this electrostatic effect is relatively weaker than that of cationic polyacrylamide, it still contributes to the adsorption process. In the case of polyolefin organic solution containing high-valent metal cations, anionic polyacrylamide will form an insoluble gel with these metal ions to achieve adsorption and removal. On the basis of adsorption complexation or adsorption bridging, the removal effect of impurities such as catalysts and ligands that have not reacted completely is further enhanced.

[0041] Preferably, the molecular weight of the anionic polyacrylamide is 26 million.

[0042] It should be noted that in the process of trying to directly contact polyacrylamide with polyolefin organic solution, it was found that polyacrylamide has poor solubility in polyolefin organic solution. Polyolefin is a type of non-polar or weakly polar polymer material, while polyacrylamide is a polymer with polar groups. The difference in polarity leads to poor compatibility between the two and difficulty in uniform mixing. In addition, polyacrylamide has a large molecular weight and a relatively stretched molecular chain. It may be affected by steric hindrance in polyolefin organic solution and is difficult to fully disperse, further reducing the compatibility between the two and making it difficult to achieve direct contact with polyolefin organic solution.

[0043] In addition, polyacrylamide is more likely to undergo cross-linking and aggregation in polyolefin organic solutions. The reason is that polyacrylamide has a certain degree of adhesion, and polyacrylamide may undergo cross-linking reactions with other components in the polyolefin glue, resulting in an increase in the viscosity of the polyolefin organic solution, an acceleration of the curing speed, and even a gel phenomenon. At the same time, polyacrylamide is prone to agglomeration in polyolefin organic solutions to form larger particles or agglomerates. This is because there are interactions such as hydrogen bonds between polyacrylamide molecules, which make it easy to aggregate together in polyolefin organic solutions, making the adsorption and removal effect of polyacrylamide worse.

[0044] Based on the above problems, the direct contact of the present invention specifically includes configuring polyacrylamide into an aqueous solution, contacting it with a polyolefin organic solution through water washing; preparing a packed column using polyacrylamide as a filler, and contacting it with the polyolefin organic solution through the packed column. Dissolve polyacrylamide in water, and the polyacrylamide will fully stretch in water to expose a large number of amide groups. Mix the polyacrylamide aqueous solution with the polyolefin organic solution. Due to the incompatibility of the two solutions, the amide groups of polyacrylamide tend to interact with polar impurities in the polyolefin organic solution to form adsorption complexes or adsorption bridges. Load polyacrylamide into a column as a filler to form a packed column. Polyacrylamide forms a fixed bed in the column, providing a large amount of adsorption surface area. After the polyolefin organic solution flows out through the packed column, impurity particles or molecules such as catalysts and ligands that have not reacted completely will contact the polyacrylamide solid in the column. Due to hydrogen bond interactions and adsorption such as van der Waals forces, adsorption complexes are formed, so that the particles or molecules are fixed on the surface of the polyacrylamide, thereby achieving purification of the polyolefin organic solution. Through the above two direct contact methods, the problems of poor solubility of polyacrylamide in polyolefin organic solution and easy cross-linking and aggregation can be taken into account.

[0045] According to an embodiment of the present invention, in the case where the direct contact is to configure polyacrylamide into an aqueous solution and contact it with a polyolefin organic solution by washing with water, the method includes: passing the aqueous solution of polyacrylamide into the polyolefin organic solution and stirring and mixing to perform a direct contact operation; performing two-phase separation between the polyolefin organic solution after impurities are removed and the aqueous solution of polyacrylamide to obtain a purified polyolefin organic solution. The polyacrylamide is completely dissolved in water to form an aqueous solution, and the obtained polyacrylamide aqueous solution is stirred to fully contact the polyolefin organic solution during the mixing process with the polyolefin organic solution, ensuring that the amide group of the polyacrylamide can fully interact with the impurity molecules such as the catalyst and ligand that have not reacted completely in the polyolefin organic solution, and the impurity molecules are adsorbed and removed from the polyolefin organic solution, and then separated by two-phase separation means such as sedimentation, centrifugation or filtration to obtain a purified polyolefin organic solution.

[0046] Specifically, when the aqueous solution of polyacrylamide is passed into the polyolefin organic solution and stirred and mixed, the temperature of stirring and mixing is 80-120°C, for example, 80°C, 90°C, 100°C, 110°C or 120°C, preferably 75°C. The time of stirring and mixing is 5-30min, for example, 5min, 10min, 15min, 20min, 25min or 30min, preferably 15min. The speed of stirring and mixing is 1000-3000rpm, preferably 2000rpm. The rate of passing the aqueous solution of polyacrylamide is 10-100mL / min, for example, 10mL / min, 20mL / min, 30mL / min, 40mL / min, 50mL / min, 60mL / min, 70mL / min, 80mL / min, 90mL / min or 100mL / min, preferably 20mL / min. For example, the aqueous solution of polyacrylamide can be mixed with the polyolefin organic solution by a horizontal flow pump. The volume ratio of the polyolefin organic solution to the polyacrylamide aqueous solution is (5-15):1, for example, 5:1, 7:1, 9:1, 11:1, 13:1 or 15:1. In the relevant experiments of the present invention, it is found that adjusting the relevant parameters of stirring and mixing within the above ranges is helpful to promote the full contact between the polyacrylamide and the polyolefin organic solution, so that the adsorption is more thorough, and the removal effect of impurities such as unreacted catalysts and ligands is relatively better.

[0047] More specifically, the mass fraction of polyacrylamide in the aqueous solution of polyacrylamide is 0.01-5%, for example, it can be 0.01%, 1%, 2%, 3%, 4% or 5%, preferably 0.05%. When the mass fraction of polyacrylamide in the aqueous solution of polyacrylamide is too low, the number of polyacrylamide molecules in the aqueous solution is relatively small, and the adsorption bridging effect is limited. Because adsorption bridging is fixed on different particle surfaces by polyacrylamide molecular chains, polymer bridges are formed between each particle, so that the particles form aggregates and settle. If the concentration is too low, the molecular chains are sparsely distributed in the water, and there are fewer opportunities to contact and connect particles, making it difficult to effectively gather more suspended particles together. A small amount of polyacrylamide molecules cannot fully play their role, so that the electrostatic repulsion between particles is still large, and it is impossible to effectively condense, resulting in an insignificant flocculation effect. When the mass fraction of polyacrylamide is too high, the viscosity of the aqueous solution of polyacrylamide will increase significantly, and reflocculation may also occur. Due to the excessive number of polyacrylamide molecules, a large number of polymer molecules will continue to be adsorbed on the surface of the flocs that have been flocculated, causing the surface charge of the flocs to change, resulting in the flocs attracting each other again and flocculating, making the flocs too large and uneven, affecting their sedimentation performance, and may even clog the filtration equipment and increase energy consumption during the treatment process. At the same time, using too high a concentration of polyacrylamide will also increase costs.

[0048] When the mass fraction of polyacrylamide is within the appropriate range, polyacrylamide can give full play to its flocculation effect. The polar groups on its molecular chain can adsorb solid particles suspended in water, and connect multiple particle impurities through adsorption bridging to form larger flocs. It can better neutralize the surface charge of particle impurities. The zeta potential on the particle surface is the reason for particle inhibition. Polyacrylamide reduces the zeta potential and condenses through its own charge properties (such as anionic polyacrylamide can neutralize the surface charge of positively charged particles). Moderate concentration can ensure that a sufficient number of polyacrylamide interacts with particle impurities to achieve charge neutralization, thereby accelerating the sedimentation of particle impurities. In addition, the polyacrylamide solution at a moderate concentration has a sufficient number of molecules to provide adsorption sites. The amide groups in its molecular chain are easy to adsorb on the surface of impurities such as silt particles by hydrogen bonding. And because of the long molecular chain, there is a huge adsorption surface area, which can effectively adsorb impurities in water.

[0049] According to the embodiments of the present invention, polyacrylamide is easily soluble in water and can quickly form a uniform solution in water. During the dissolution process, its molecular chain fully stretches, exposing more adsorption sites, providing favorable conditions for adsorbing impurities in polyolefin glue. The polyacrylamide molecular chain contains amide groups, which enables the polyacrylamide adsorbent to interact with suspended particles, colloids and other substances in water, and achieve adsorption and flocculation effects through charge neutralization, adsorption bridging, surface adsorption and other mechanisms.

[0050] In one specific embodiment, the process of preparing polyacrylamide into an aqueous solution and contacting it with a polyolefin organic solution by water washing is as follows:

[0051] Add polyacrylamide to water, preferably pure water, and stir the mixture at 75° C. and 2000 rpm for 15 minutes to prepare an aqueous solution of polyacrylamide with a mass percentage of 0.05%.

[0052] Ethylene is used as a comonomer, a polymerization reaction is carried out under the catalytic action of α-diimine nickel catalyst and diethylaluminum chloride, n-heptane is used as a polymerization solvent, the reaction temperature is 35-80°C, the reaction pressure is 0.5-5MPa, the reaction time is 20-60min, and a polyolefin glue is prepared.

[0053] The polyacrylamide solution is added to a U-tube mixer at a rate of 20 mL / min through a horizontal flow pump and a polyolefin glue solution at a ratio of 1:10 through different delivery pipes, and then transported to a water washing tank. The spiral stirring speed is set to 1000-3000 rpm in the range of 80-120° C. and the mixture is fully stirred for 5-30 minutes. The aqueous phase and the glue solution phase are separated by standing in a three-stage separator, and the polyacrylamide aqueous solution in the lower layer is discharged from the water outlet at the lower end of the separator and introduced into a recovery tank for recycling. The polyolefin glue solution in the upper layer is continuously transported from the side of the separator to a flash tank, and is discharged and granulated after removing excess solvent to prepare a polyolefin elastomer.

[0054] According to an embodiment of the present invention, in the case where direct contact is to prepare a filling column using polyacrylamide as a filler and contact the polyolefin organic solution through the filling column, separation includes: the polyolefin organic solution flows out after passing through a solid column filled with polyacrylamide to obtain a purified polyolefin organic solution. Polyacrylamide has a high degree of polymerization and a high molecular weight. The high degree of polymerization enables it to have a spatial network of molecular chains intertwined with each other, and the large molecular weight enables it to better interact with impurity molecules and enhance the adsorption effect.

[0055] According to an embodiment of the present invention, the volume of polyacrylamide in the solid column filled with polyacrylamide is 60-95% of the volume of the solid column, for example, 60%, 70%, 80%, 90% or 95%.

[0056] The solid column is also filled with ceramic balls, which can be any commercially available source and have a particle size of 3-5 mm, preferably 3 mm; the volume of the ceramic balls is 5-40% of the volume of the solid column; the upper and lower ends of the solid column also include filling layers of ceramic balls respectively.

[0057] It was found during the relevant experiments of the present invention that due to the adhesiveness of polyacrylamide, it is easy to undergo cross-linking reaction with some components in the polyolefin organic solution, which increases the viscosity of the polyolefin organic solution, makes it easy to solidify, and polyacrylamide is easy to agglomerate in the polyolefin organic solution. This makes it difficult for polyacrylamide to exert its adsorption effect, and may also affect the fluidity of the polyolefin organic solution and cause the solid column to be blocked. Therefore, in the process of filling, it is necessary to add the above-mentioned proportion of ceramic balls for mixed filling to improve the dispersion of polyacrylamide, which is conducive to the flow of the polyolefin organic solution and improves the adsorption efficiency.

[0058] It should be noted that when filling the solid column, 3-5 mm ceramic balls are used to set up filling layers at the upper and lower ends to reduce the clogging of the feed port and the discharge port.

[0059] According to an embodiment of the present invention, when the polyolefin organic solution passes through a solid column filled with polyacrylamide, the temperature is 80-120°C, for example, 80°C, 90°C, 100°C, 110°C or 120°C, and the temperature is kept for 10-60 minutes, and the pressure is 0.1-1 MPa. By controlling the temperature, temperature holding time and pressure of the polyolefin organic solution flowing through the solid column, the polyolefin organic solution is ensured to have good fluidity.

[0060] In one specific embodiment, polyacrylamide is used as a filler to prepare a packed column, and the method for removing impurities such as unreacted catalysts and ligands in a polyolefin organic solution through the packed column comprises:

[0061] Filling the polyacrylamide solid column: Add 3~5mm small ceramic balls with a volume fraction of 5-40% according to the total volume of the polyacrylamide solid. When filling the solid column, the upper and lower filling layers are single 3~5mm ceramic balls, and the middle of the upper filling layer and the lower filling layer is a mixed filling layer of polyacrylamide and ceramic balls.

[0062] Ethylene is used as a comonomer, a polymerization reaction is carried out under the catalytic action of α-diimine nickel catalyst and diethylaluminum chloride, n-heptane is used as a polymerization solvent, the reaction temperature is 35-80°C, the reaction pressure is 0.5-5MPa, the reaction time is 20-60min, and a polyolefin glue is prepared.

[0063] The polyolefin glue in the reaction tank is directly transported to the polyacrylamide solid column after heating and heat preservation. The temperature of the polyolefin glue is in the range of 60-100℃. The heating belt and heat preservation cotton are wrapped around the solid column. The column is kept at 80-120℃ for 10-60 minutes for full adsorption. The outflowing polyolefin solution is directly transported to the flash tank.

[0064] Based on the above two methods of direct contact through water washing and using polyacrylamide as a solid column, by using polyacrylamide adsorbent to treat the polyolefin organic solution, impurities such as catalysts and ligands that have not reacted completely in the polyolefin organic solution can be effectively removed, so that the ultraviolet and visible light transmittance of the finally prepared polyolefin elastomer is effectively improved, and the volume resistivity of the polymer is effectively increased, and the yellowness index of the polymer is reduced.

[0065] The present invention is further described below by examples and related test experiments. In the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is obvious that one or more embodiments may also be implemented without these specific details. And, in the absence of conflict, the details in the following embodiments may be combined into other feasible embodiments at will. All instruments, consumables and reagents in the following examples, if not otherwise specified, may be obtained from commercial sources.

[0066] Embodiment 1:

[0067] Prepare polyacrylamide solution: Take 1 L of pure water, weigh 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 5%, and 7% of anionic polyacrylamide (particle size: 100 μm), stir at 2000 rpm at 35°C for 15 min, and let stand for use.

[0068] Ethylene was used as a comonomer, and a polymerization reaction was carried out under the catalysis of α-diimine nickel catalyst and diethylaluminum chloride. n-heptane was used as a polymerization solvent. The reaction temperature was 55° C., the reaction pressure was 3 MPa, and the reaction time was 30 min to prepare a polyolefin glue.

[0069] Anionic polyacrylamide with molecular weights of 10 million and 26 million were selected to prepare solutions, which were mixed with polyolefin glue in a U-tube mixer at a ratio of 1:10 at a rate of 20 mL / min using a horizontal flow pump, and then transported to a washing tank. They were fully stirred for 30 minutes at 80°C, and then passed through a three-stage separator for static separation. The polyolefin solution was transported to a flash tank, and the separated polyacrylamide aqueous solution was recycled.

[0070] The treated glue solution was rotary evaporated and then pressed into film, and its ultraviolet and visible light transmittance, yellowness index and volume resistivity were tested. The results are shown in Tables 1 and 2 below.

[0071] Table 1 Results of anionic polyacrylamide washing solution (molecular weight 10 million)

[0072]

[0073] Table 2 Results of anionic polyacrylamide washing solution (molecular weight 26 million)

[0074]

[0075] As can be seen from the comparison between Table 1 and Table 2, the visible light and ultraviolet light transmittance and volume resistivity of the polyolefin elastomer after washing with the anionic polyacrylamide washing solution with a molecular weight of 26 million are generally higher than those of the polyolefin elastomer after washing with the anionic polyacrylamide washing solution with a molecular weight of 10 million at the same mass fraction, and the yellowness index of the polyolefin elastomer prepared using the anionic polyacrylamide with a molecular weight of 26 million is lower than that using the anionic polyacrylamide with a molecular weight of 10 million, indicating that the anionic polyacrylamide with a molecular weight of 26 million is relatively better in removing impurities such as catalysts and ligands that have not reacted completely in the polyolefin glue.

[0076] Embodiment 2:

[0077] Prepare polyacrylamide solution: Take 1L of pure water, weigh 0.05% of cationic polyacrylamide (particle size 300μm), stir at 2000rpm for 15min at 75℃, and let it stand for use.

[0078] The process of preparing the polyolefin adhesive in this embodiment 2 is substantially the same as that in embodiment 1, and will not be described again here.

[0079] Cationic polyacrylamide with molecular weights of 100,000, 400,000, 700,000, 6 million, 10 million, 24 million, and 30 million, and nonionic polyacrylamide with molecular weights of 8 million and 10 million were selected to prepare aqueous solutions of polyacrylamide, which were mixed with polyolefin glue in a U-tube mixer at a rate of 1:10 at a rate of 20 mL / min using a horizontal flow pump, and transported to a washing tank. They were fully stirred for 30 minutes at 80°C, and then statically separated in a three-stage separator. The polyolefin solution was transported to a flash tank, and the separated polyacrylamide aqueous solution was recycled.

[0080] The treated polyol solution was subjected to rotary evaporation and then pressed into a film, and its ultraviolet and visible light transmittance, yellowness index and volume resistivity were tested. The results are shown in Tables 3 and 4 below.

[0081] Table 3 Cationic polyacrylamide washing solution results

[0082]

[0083] Table 4 Nonionic polyacrylamide washing solution results

[0084]

[0085] Comparing the data in Table 3, the effect of cationic polyacrylamide cleaning solution with a molecular weight of 700,000 is relatively better. By comparing Table 3 and Table 4 with a molecular weight of 10 million, it can be seen that the removal effect of cationic polyacrylamide is better than that of non-ionic polyacrylamide. The reason is that cationic polyacrylamide can attract negatively charged impurity particles to form electrostatic attraction, which further promotes the aggregation of impurity particles.

[0086] According to the data in Table 3, the mass fraction of polyacrylamide in the cationic polyacrylamide aqueous solution was further adjusted, and the above-mentioned steps of washing the glue solution were repeated to find the mass fraction of polyacrylamide with the best effect (which can be understood as the mass concentration of polyacrylamide).

[0087] Embodiment 3:

[0088] Prepare polyacrylamide solution: Take 1L of pure water, weigh 0.01%, 0.05%, 0.1% and 0.5% of cationic polyacrylamide (particle size 300μm), stir at 2000rpm at 75℃ for 15min, and let stand for use.

[0089] The process of preparing the polyolefin glue in this embodiment 3 is substantially the same as that in embodiment 1, and will not be described again here.

[0090] Cationic polyacrylamide with a molecular weight of 700,000 was selected to prepare a solution, which was mixed with polyolefin glue in a U-tube mixer at a ratio of 1:10 at a rate of 20 mL / min through a horizontal flow pump, and then transported to a water washing tank. It was fully stirred for 30 minutes at 80°C, and then statically separated in a three-stage separator. The polyolefin solution was transported to a flash tank, and the separated polyacrylamide aqueous solution was recycled.

[0091] The treated glue solution was rotary evaporated and then pressed into film, and its ultraviolet and visible light transmittance, yellowness index and volume resistivity were tested. The results are shown in Table 5 below.

[0092] Table 5 Results of different concentrations of cationic polyacrylamide washing solutions

[0093]

[0094] As shown in Table 5, the cationic polyacrylamide aqueous solution with a concentration of 0.01% has a relatively better effect on removing impurities.

[0095] Embodiment 4:

[0096] Anionic polyacrylamide solid columns were filled, and anionic polyacrylamide with molecular weights of 10 million and 26 million were selected respectively. 3 mm small ceramic balls were added at a volume fraction of 15%. Heating tape and thermal insulation cotton were wrapped around the solid column and heated to 90°C for insulation.

[0097] The process of preparing the polyolefin glue in this embodiment 4 is substantially the same as that in embodiment 1, and will not be described again here.

[0098] The polyolefin glue solution is directly transported to the polyacrylamide solid column, kept at 90°C for 25 minutes for sufficient adsorption, and the outflowing polyolefin solution is transported to the flash tank.

[0099] The treated glue solution was rotary evaporated and then pressed into film, and its ultraviolet and visible light transmittance, yellowness index and volume resistivity were tested. The results are shown in Table 6 below.

[0100] Table 6 Anionic polyacrylamide filler column results

[0101]

[0102] As shown in Table 6, the anionic polyacrylamide filler with a molecular weight of 26 million has a relatively better effect on removing impurities when passed through the column.

[0103] Embodiment 5:

[0104] Fill a cationic polyacrylamide solid column, select cationic polyacrylamide with molecular weights of 100,000, 400,000, 700,000, 6 million, 10 million and 24 million, and non-ionic polyacrylamide with molecular weights of 8 million and 10 million, add 15% of 3 mm small ceramic balls, wrap heating tape and thermal insulation cotton around the solid column, and heat to 90°C for insulation.

[0105] The process of preparing the polyolefin glue in this embodiment 5 is substantially the same as that in embodiment 1, and will not be described again here.

[0106] The polyolefin glue solution is directly transported to the polyacrylamide solid column, kept at 90°C for 25 minutes for sufficient adsorption, and the outflowing polyolefin solution is transported to the flash tank.

[0107] The treated glue solution was rotary evaporated and then pressed into film, and its ultraviolet and visible light transmittance, yellowness index and volume resistivity were tested. The results are shown in Tables 7 and 8 below.

[0108] Table 7 Cationic polyacrylamide filler column results

[0109]

[0110] Table 8 Results of nonionic polyacrylamide filler column

[0111]

[0112] According to the data comparison in Table 7, although the light transmittance of the polyolefin elastomer prepared by the cationic polyacrylamide washing solution with a molecular weight of 700,000 is weaker than that of 6 million and 24 million, its yellowness index and volume resistivity are better than those of other molecular weight products, and can be selected accordingly according to different needs for products. According to the horizontal comparison in Tables 7 and 8 with a molecular weight of 10 million, cationic polyacrylamide has stronger ultraviolet light transmittance and yellowness index, and weaker light transmittance and volume resistivity under visible light than non-ionic polyacrylamide. The reason may be that cationic polyacrylamide carries positively charged groups on the molecular chain, and these charged groups will produce specific absorption and scattering effects on ultraviolet light. The cationic groups in its molecular structure may form a conjugated system or a change in the distribution of the electron cloud, so that it has better light transmittance in the ultraviolet region. And because cationic polyacrylamide carries positive charges, these charges will be conducted between molecular chains under the action of the electric field, resulting in a lower volume resistivity. Non-ionic polyacrylamide has no movable ionic charge, and the conduction of electrons on the molecular chain is relatively difficult, so the volume resistivity is higher.

[0113] In summary of the above embodiments 1 to 5, the method of the present invention uses different types of polyacrylamide adsorbents to treat polyolefin glue by washing the glue and passing through a column, which can effectively remove impurities such as catalysts and ligands that have not reacted completely in the glue, and improve the quality and stability of the polyolefin glue. In addition, the polyacrylamide used in the method has a low cost, and the treatment method is simple to operate, and has a good application prospect in process production.

[0114] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for removing impurities from a polyolefin organic solution, characterized in that: The method comprises: The polyacrylamide is directly contacted with the polyolefin organic solution, so that the impurities in the polyolefin organic solution are removed through adsorption complexation or adsorption bridging of the polyacrylamide; The polyolefin organic solution after impurities are removed is separated from the polyacrylamide to obtain a purified polyolefin organic solution.

2. The method according to claim 1, characterized in that The polyacrylamide includes at least one of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide; The molecular weight of polyacrylamide is 10~30 million.

3. The method according to claim 1, characterized in that The direct contact comprises preparing polyacrylamide into an aqueous solution and contacting the aqueous solution with the polyolefin organic solution by washing with water; or A packed column is prepared by using polyacrylamide as a filler, and the packed column is contacted with a polyolefin organic solution.

4. The method according to claim 3, characterized in that Contact with polyolefin organic solution by water washing includes: The aqueous solution of polyacrylamide is introduced into the polyolefin organic solution and stirred to mix, so as to perform the direct contact operation.

5. The method according to claim 4, characterized in that When the aqueous solution of polyacrylamide is introduced into the polyolefin organic solution and stirred and mixed, the stirring and mixing temperature is 80-120° C., and the stirring and mixing time is 5-30 min; The rate of introduction of the aqueous solution of polyacrylamide is 10-100 mL / min; The volume ratio of the polyolefin organic solution to the polyacrylamide aqueous solution is (5-15):1; The mass fraction of polyacrylamide in the aqueous solution of polyacrylamide is 0.01~5%.

6. The method according to claim 3, characterized in that: In the case of preparing a packed column using polyacrylamide as a filler, the separation comprises: The polyolefin organic solution is passed through a solid column filled with polyacrylamide and then flows out to obtain a purified polyolefin organic solution.

7. The method according to claim 6, characterized in that The volume of polyacrylamide in the solid column filled with polyacrylamide is 60-95% of the volume of the solid column; The solid column is also filled with ceramic balls, and the particle size of the ceramic balls is 3-5 mm; The volume of the ceramic balls is 5-40% of the volume of the solid column; The upper and lower ends of the solid column also include filling layers of ceramic balls respectively.

8. The method according to claim 6, characterized in that When the polyolefin organic solution passes through the solid column filled with polyacrylamide, the temperature is 80-120° C., the temperature is kept for 10-60 minutes, and the pressure is 0.1-1 MPa.

9. The method according to claim 1, characterized in that: The polyolefin organic solution is prepared by the following method: Adding comonomer, main catalyst and co-catalyst into an organic solvent to carry out polymerization reaction to obtain a polyolefin organic solution; The organic solvent includes one or more of n-hexane, isobutane, isopentane, n-heptane, n-octane, isooctane, toluene and dichloromethane; The comonomer includes ethylene; The main catalyst includes an α-diimine nickel catalyst; The co-catalyst includes one or more of diethylaluminum chloride and triethylaluminum chloride; The polymerization reaction temperature is 35-80° C., the polymerization reaction time is 20-60 min, and the polymerization reaction pressure is 0.5-5 MPa.

10. The method according to claim 1, characterized in that The polyolefin is a polyolefin elastomer, the polyolefin organic solution is a polyolefin glue, and the impurities include ligands decomposed by the main catalyst during the reaction, unreacted main catalyst and unreacted co-catalyst.

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