In-situ nucleated polypropylene and preparation method thereof

Abstract

The present invention provides an in-situ nucleated polypropylene and a preparation method thereof. A titanium-containing main catalyst, a co-catalyst, and a nucleating agent monomer are added into a reaction kettle, and then a solvent is added to react to obtain a catalyst loaded with a polymer nucleating agent; the co-catalyst, an external electron donor, and the catalyst loaded with a polymer nucleating agent are mixed, and gas phase propylene is introduced to perform propylene slurry prepolymerization; after the prepolymerization is completed, the solvent is separated, and liquid phase propylene and hydrogen are introduced to perform bulk polymerization to obtain in-situ nucleated polypropylene. After the polymer nucleating agent is prepared in one step, gas phase propylene is directly introduced to perform slurry prepolymerization, so that the catalyst releases active centers to the maximum extent to improve its catalytic activity in bulk polymerization, and the in-situ nucleated polypropylene containing a low concentration of polymer nucleating agent exhibits a higher crystallization temperature and crystallinity. The crystallization temperature of the in-situ nucleated polypropylene is higher than 128°C, and the crystallinity is greater than 55%; the concentration of the polymer nucleating agent in the in-situ nucleated polypropylene is 20-30ppm.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to in-situ nucleated polypropylene and a preparation method thereof. Background Art

[0002] Polypropylene has excellent physical, mechanical and chemical properties. However, since polypropylene is a semi-crystalline polymer, it has the disadvantages of slow crystallization rate, low crystallinity, and easy formation of large-sized spherulites during the molding process, which greatly limits its performance and application. The method of adding nucleating agents to polypropylene to improve the above-mentioned disadvantages is well known in the art.

[0003] The nucleating agents used in the in-situ nucleation technology can be divided into conventional nucleating agents and polymer nucleating agents. In the research on conventional nucleating agent in-situ nucleation technology, patents US 2013 / 0190435A1 and WO 2015 / 021948A1 of the Brno Polymer Research Institute of the Czech Petrochemical Industry publicly reported that nucleating agents prepared by reacting alkyl aluminum with compounds of aliphatic or aromatic carboxylic acid amide derivatives were used for in-situ nucleation; patent CN102603941B of Dong Jinyong's research team of the Institute of Chemistry of the Chinese Academy of Sciences reported that a catalyst with a conventional β-nucleating agent as a carrier catalyzed propylene polymerization, and the role of the catalyst carrier ensured the good dispersion of the nucleating agent in the polypropylene matrix; Niu Hui's research team of Dalian University of Technology made the mature purchased nucleating agent into a component inert to the catalyst, and added it together with the catalyst during polymerization. Compared with the traditional processing nucleation method, the amount of nucleating agent added was reduced; patent CN 1974611A of Xin Zhong's team of East China University of Science and Technology reported a preparation method and application of a nucleating agent for polyolefins with catalytic function; patent CN 101735354B and CN103524644B reported adding rare earth β-type nucleating agents to the catalytic system for in-situ nucleation of polypropylene. Although the conventional in-situ nucleation technology of nucleating agents can achieve a good nucleation effect at a concentration below 500ppm and is more evenly dispersed in the polymer compared to the traditional processing nucleation technology, the technology requires the nucleating agent to be inert, which has a high processing cost and reduces the catalytic activity of the catalytic system.

[0004] In the research on in-situ nucleation technology of polymer nucleating agents, in the in-situ nucleation technology of Borealis, propylene bulk prepolymerization is adopted after the catalyst modification is completed, and the concentration of in-situ polymer nucleating agent is still 45-1000ppm; and the catalyst modification process is complicated, and the catalyst modification and main polymerization reaction are discontinuous, which will cause a certain degree of catalyst loss, thereby affecting the catalytic activity of the system. Summary of the invention

[0005] In view of this, an object of the present invention is to provide an in-situ nucleated polypropylene and a preparation method thereof. The in-situ nucleated polypropylene prepared by the method has a higher crystallization temperature and crystallinity.

[0006] The present invention provides a method for preparing in-situ nucleated polypropylene, comprising the following steps:

[0007] 1) Adding a titanium-containing main catalyst, a co-catalyst, and a nucleating agent monomer into a reaction kettle, and then adding a solvent, reacting to obtain a catalyst loaded with a polymer nucleating agent;

[0008] 2) Mixing the co-catalyst, the external electron donor and the catalyst loaded with the polymer nucleating agent, and introducing gas phase propylene to carry out propylene slurry prepolymerization;

[0009] 3) After the prepolymerization, the solvent is separated, and then liquid propylene and hydrogen are introduced to carry out bulk polymerization to obtain in-situ nucleated polypropylene.

[0010] In the present invention, the main catalyst is a magnesium chloride-supported titanium tetrachloride spherical catalyst, namely a Ziegler-Natta catalyst; the magnesium chloride-supported titanium tetrachloride spherical catalyst is selected from one or more of the N series, DQ series, CS series, STP series and TK series propylene polymerization catalysts.

[0011] The co-catalyst is an alkyl aluminum compound; the alkyl aluminum compound is selected from one or more of triethyl aluminum, triisobutyl aluminum, trihexyl aluminum, trioctyl aluminum, diethyl aluminum monochloride, diisobutyl aluminum monochloride, dihexyl aluminum monochloride and dioctyl aluminum monochloride;

[0012] The nucleating agent monomer is selected from vinyl compounds; the vinyl compound is selected from one or more of vinyl cyclohexane, vinyl cyclopentane, vinyl-2-methylcyclohexane, 3-methyl-1-butene, 3-ethyl-1-hexene, 3-methyl-1-pentene and styrene;

[0013] The external electron donor is selected from a silane compound; the silane compound is selected from vinyl triethoxysilane, vinyl trimethoxysilane, methyl triethoxysilane, dimethyl dimethoxysilane, diethyl dimethoxysilane, dipropyl dimethoxysilane, diisopropyl dimethoxysilane, dibutyl dimethoxysilane, diisobutyl dimethoxysilane, di-tert-butyl dimethoxysilane, di-tert-hexyl dimethoxysilane, diphenyl dimethoxysilane, dicyclohexyl dimethoxysilane, dicyclopentyl dimethoxysilane, dimethyl diethoxysilane, diethyl diethoxysilane, dipropyl One or more of diethoxysilane, diisopropyldiethoxysilane, dibutyldiethoxysilane, diisobutyldiethoxysilane, di-tert-butyldiethoxysilane, di-tert-hexyldiethoxysilane, diphenyldiethoxysilane, dicyclohexyldiethoxysilane, dicyclopentyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, cyclopentylmethyldimethoxysilane, cyclopentyltrimethoxysilane, cyclohexylmethyldimethoxysilane, cyclohexyltrimethoxysilane, tert-hexyltrimethoxysilane, tert-butyltrimethoxysilane, and tert-hexyltrimethoxysilane;

[0014] The solvent is an alkane; the alkane is selected from one or more of n-pentane, isopentane, n-hexane, n-heptane and n-octane.

[0015] In the present invention, during the reaction process of step 1), the tetravalent titanium on the surface of the titanium-containing main catalyst is reduced to trivalent titanium by the co-catalyst, and participates in the polymerization reaction of the nucleating agent monomer; the content of activated titanium in the titanium-containing main catalyst accounts for 1-10% of the total titanium in the titanium-containing main catalyst, preferably 1-5%; the surface of the catalyst loaded with polymer nucleating agent obtained by the reaction is polymer nucleating agent; the mass of the polymer nucleating agent in the catalyst loaded with polymer nucleating agent accounts for 20-80%.

[0016] In the present invention, the molar ratio of the co-catalyst to the titanium in the titanium-containing main catalyst in step 1) is 1 to 100:1;

[0017] The molar ratio of the co-catalyst in step 2) to the titanium in the titanium-containing main catalyst in step 1) is 20 to 300:1;

[0018] The molar ratio of the external electron donor in step 2) to the titanium in the titanium-containing main catalyst in step 1) is 5 to 30:1;

[0019] The mass ratio of the nucleating agent monomer to the titanium-containing main catalyst in step 1) is 0.5 to 5:1;

[0020] In the step 1), the mass ratio of the titanium-containing main catalyst to the volume ratio of the solvent is (0.1-10) mg:1 ml;

[0021] The pressure of gaseous propylene in step 2) is 0.1-0.5 MPa.

[0022] In the present invention, the molar ratio of the liquid propylene to the titanium in the titanium-containing main catalyst in step 1) is 1×10 5 ~1×10 7 :1, hydrogen partial pressure is 0.5~5bar.

[0023] In the present invention, the reaction temperature of step 1) is 0 to 50°C and the reaction time is 5 to 20 hours;

[0024] The prepolymerization temperature in step 2) is 10 to 80° C., and the prepolymerization time is 3 to 60 minutes;

[0025] The temperature of the bulk polymerization in step 3) is 60-100° C., and the time of the bulk polymerization is 1-5 hours.

[0026] The present invention provides an in-situ nucleated polypropylene, which is prepared by the preparation method described in the above technical solution;

[0027] The in-situ nucleated polypropylene has a crystallization temperature higher than 128°C and a crystallinity higher than 55%;

[0028] The concentration of the polymer nucleating agent in the in-situ nucleated polypropylene is 20-30 ppm.

[0029] The present invention provides a method for preparing in-situ nucleated polypropylene, comprising the following steps: adding a titanium-containing main catalyst, a co-catalyst, and a nucleating agent monomer into a reactor, then adding a solvent, reacting, and obtaining a catalyst loaded with a polymer nucleating agent; mixing the co-catalyst, an external electron donor, and the catalyst loaded with a polymer nucleating agent, introducing gas phase propylene, and performing propylene slurry prepolymerization; separating the solvent after the prepolymerization, and then introducing liquid phase propylene and hydrogen for bulk polymerization to obtain in-situ nucleated polypropylene. After the catalyst loaded with a polymer nucleating agent is prepared in one step, gas phase propylene is directly introduced for slurry prepolymerization, so that the catalyst particles are fully broken to release the active center to the maximum extent to improve the catalytic activity of the catalyst in the bulk polymerization of propylene, and the finally prepared in-situ nucleated polypropylene containing a low concentration of polymer nucleating agent exhibits a higher crystallization temperature and crystallinity. Experimental results show that the crystallization temperature of the in-situ nucleated polypropylene is higher than 128°C, and the crystallinity is greater than 55%; the concentration of the polymer nucleating agent in the in-situ nucleated polypropylene is 20-30ppm. DETAILED DESCRIPTION

[0030] In order to further illustrate the present invention, an in-situ nucleated polypropylene and a preparation method thereof provided by the present invention are described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Unless otherwise specified, the methods and devices used in the present invention are conventional methods and devices in the art.

[0032] The content of polyvinylcyclohexane (PVCH) in the polymer is calculated by testing the conversion rate of vinylcyclohexane (VCH). The amount of residual VCH in the normal hexane mixture is analyzed by gas chromatograph. Toluene is used as an internal standard. The residual amount of VCH in the following examples and comparative examples is 0.

[0033] The test conditions for the polymers are as follows:

[0034] Melt mass flow rate (MFR): measured according to GB / T3682.1-2018, load 2.16kg, test temperature 230℃.

[0035] Isotacticity (C7-ins): Determined by n-heptane extraction method (n-heptane boiling extraction 8h): 2g of dry polymer sample is placed in a Soxhlet extractor and extracted with boiling n-heptane for 8h. The residue is dried to constant weight. The ratio of the polymer mass (g) to 2 (g) is the isotacticity.

[0036] DSC test: In a nitrogen atmosphere, 5-10 mg of sample was first heated from room temperature to 200°C at a rate of 10°C / min and kept at 200°C for 5 minutes to eliminate the thermal history; then, the sample was cooled to room temperature at a rate of -10°C / min; finally, the sample was reheated to 200°C at a rate of 10°C / min. The melting point (T) of the sample was calculated using the second heating curve according to the following relationship. c ) and crystallinity (X c ), melting point (T m ) is also measured according to the secondary heating curve: Xc (%) = ΔH m / ΔH * f 100%, where ΔH m is the melting enthalpy of the quadratic heating curve, ΔH * f is the standard melting enthalpy of polypropylene (165.5 J / g).

[0037] The catalytic activity is calculated according to the following formula: CA = Q / W Ti t*10 -3 , kgPP·(gTi·h) -1 , where CA is the catalytic activity of the catalyst, Q is the mass of the polymerization product (g), W Ti is the amount of catalyst titanium used (g), and t is the propylene polymerization time (h).

[0038] For ease of description, in the following embodiments, the main catalyst used is a commercially available magnesium chloride-supported titanium tetrachloride type, such as the CS series of Liaoning Xiangyang Science and Technology Chemical Group Catalyst Company, with a titanium content of 2.3wt%; the co-catalyst is triethylaluminum, which is prepared into a n-hexane solution with a concentration of 1 mol / L; the external electron donor is cyclohexylmethyldimethoxysilane (Donor-C) and dicyclopentyldimethoxysilane (Donor-D) prepared into a n-heptane solution, with a concentration of 0.2 mol / L; the polymer nucleating agent monomer is vinyl cyclohexane, with a density of 0.805 g / ml, a purity of ≥98%, and a water content of ≤100 ppm; the n-hexane has been refined to remove moisture and impurities; the propylene polymerization reaction device is a 3L high-pressure polymerization kettle, and the distance between its stirring paddle and the bottom of the polymerization kettle is 1 to 3 mm.

[0039] Comparative Example 1

[0040] After the 3-liter autoclave was fully replaced with high-purity nitrogen, 10 mg of the main catalyst, 1 ml of the co-catalyst, and 0.5 ml of the external electron donor Donor-C were added to the reactor in sequence, and then 100 ml of n-hexane was added, and gaseous propylene was continuously introduced into the reactor, and the pressure of the polymerization reactor was maintained at 0.4 MPa, and slurry polymerization was carried out at 30°C for 10 minutes; then, the reactor was evacuated at 30°C by a diaphragm vacuum pump to extract and separate the solvent, and finally 700 g of liquid propylene and 1.5 bar of hydrogen were introduced into the reactor for bulk polymerization, and polymerization was carried out at 80°C for 2 hours. The results of propylene polymerization and polymer characterization are shown in Table 1.

[0041] Comparative Example 2

[0042] After the 3-liter autoclave was fully replaced with high-purity nitrogen, 10 mg of the main catalyst, 1 ml of the co-catalyst, and 0.5 ml of the external electron donor Donor-C were added to the reactor in sequence, and then 700 g of liquid propylene was added to carry out bulk prepolymerization at 30°C for 10 min; finally, 1.5 bar of hydrogen was added to the reactor for bulk polymerization, and polymerization was carried out at 80°C for 2 h. The results of propylene polymerization and polymer characterization are shown in Table 1.

[0043] Comparative Example 3

[0044] VCH modification of catalyst in n-hexane, such as patent CN 109196003B.

[0045] Add 60 ml of n-hexane and 2 ml of co-catalyst into a 250 ml glass reactor. After 20 minutes, add 0.4 g of the main catalyst, add 0.6 g of VCH within 1 hour at room temperature, polymerize at 50°C for 15 hours, and cool to room temperature. Remove most of the n-hexane in the mixture by decantation, and flush the remaining n-hexane in the mixture with nitrogen to obtain 0.95 g of the modified solid catalyst. 10 mg of the main catalyst becomes 23.75 mg after modification.

[0046] Propylene polymerization: After the 3-liter autoclave was fully replaced with high-purity nitrogen, 23.75 mg of the modified main catalyst, 0.95 ml of the co-catalyst, and 0.48 ml of the external electron donor Donor-C were added to the reactor in sequence, and then 100 ml of n-hexane was added, and gaseous propylene was continuously introduced into the reactor, and the pressure of the polymerization reactor was maintained at 0.4 MPa, and slurry polymerization was carried out at 30°C for 10 minutes; then, the reactor was evacuated at 30°C by a diaphragm vacuum pump to extract and separate the solvent, and finally 700 g of liquid propylene and 1.5 bar of hydrogen were introduced into the reactor for bulk polymerization, and the polymerization was carried out at 80°C for 2 hours. The results of propylene polymerization and polymer characterization are shown in Table 1.

[0047] Example 1

[0048] After the 3-liter autoclave was fully replaced with high-purity nitrogen, 10 mg of the main catalyst, 1 ml of the co-catalyst (the original concentration was diluted 20 times to 0.05 mol / L), 15 mg of VCH, and 100 ml of n-hexane were added in sequence, and polymerization was carried out at 30°C for 15 hours; after the polymerization, 1 ml of the co-catalyst and 0.5 ml of the external electron donor Donor-C were added to the reactor, and gaseous propylene was continuously introduced into the reactor, and the pressure of the polymerization reactor was maintained at 0.4 MPa, and slurry prepolymerization was carried out at 30°C for 10 minutes; finally, the reactor was evacuated at 30°C by a diaphragm vacuum pump to extract and separate the solvent, and then 700 g of liquid propylene and 1.5 bar of hydrogen were introduced into the reactor for bulk polymerization, and polymerization was carried out at 80°C for 2 hours. The results of propylene polymerization and polymer characterization are shown in Table 1.

[0049] Example 2

[0050] Donor-D was selected as the external electron donor, and other preparation conditions were the same as those in Example 1.

[0051] Example 3

[0052] The propylene slurry polymerization was performed for 3 min, and other preparation conditions were the same as those in Example 1.

[0053] Example 4

[0054] The propylene slurry polymerization was carried out for 6 minutes, and other preparation conditions were the same as those in Example 1.

[0055] Implementation Benefits 5

[0056] The prepolymerization time of propylene slurry was 30 min, and other preparation conditions were the same as those in Example 1.

[0057] Table 1 Characterization results of polymers of the implementation examples and comparative examples

[0058]

[0059] Note: a. The catalytic activity of Comparative Example 3 was calculated based on the main catalyst dosage of 10 mg.

[0060] Catalytic activity is one of the important properties of a catalyst. It indicates the quality of polymer that can be produced per unit amount of active component of the catalyst per unit time, and directly affects the production cost of the product. As can be seen from Table 1, compared with the liquid phase propylene bulk prepolymerization (Comparative Example 2), the catalytic activity of the gas phase propylene slurry polymerization system (such as Examples 1 to 5) is higher, which can indicate that under the same process conditions, propylene gas phase polymerization is more conducive to the fragmentation of the catalyst and the release of the active center; Example 1 shows similar catalytic activity compared with Comparative Example 1, indicating that under the same polymerization process conditions, the preparation and addition of the polymer nucleating agent of the present invention has basically no effect on the catalytic activity of the system; Example 1 has a higher catalytic activity than Comparative Example 3, indicating that the in-situ nucleation polypropylene preparation method of the present invention is more conducive to the maintenance and improvement of catalytic activity than the method reported in the previous patent; The difference in catalytic activity of Example 1, Example 3, Example 4 and Example 5 can indicate that the prepolymerization time can affect the fragmentation of the catalyst and the release of the active center. If the prepolymerization time is too short (3min, 6min), the catalyst is not completely fragmented and some active centers are not released. If the prepolymerization time is too long (30min), some active centers released by the fragmentation of the catalyst are buried in the polypropylene and cannot contact with the propylene monomer for polymerization reaction; The comparison between Example 1 and Example 2 shows that under the conditions of using different external electron donors, both show good catalytic activity.

[0061] Crystallization temperature is a good indicator of nucleating agent efficiency, and a higher crystallization temperature means more effective nucleation in the final product. It can be seen from Table 1 that Examples 1 to 5 all exhibited good nucleating effects, increasing the crystallization temperature of polypropylene from 119.7 to 119.9°C to 128.3 to 128.7°C, and the crystallinity was greater than 55%; Example 1 and Comparative Example 3 (VCH modified catalyst) prepared in-situ nucleated polypropylene under the same propylene polymerization conditions had similar nucleating agent contents, but the nucleating effect of the method of the present invention was better (128.6°C>126.4°C); It can be seen from Examples 1 to 5 that the nucleating agent concentration in the in-situ nucleated polypropylene prepared by the method of the present invention was 20 to 30 ppm, but the nucleating effect was very obvious.

[0062] As can be seen from the above embodiments, the present invention provides a method for preparing in-situ nucleated polypropylene, comprising the following steps: adding a titanium-containing main catalyst, a co-catalyst, and a nucleating agent monomer into a reactor, then adding a solvent, reacting, and obtaining a catalyst loaded with a polymer nucleating agent; mixing the co-catalyst, an external electron donor, and a catalyst loaded with a polymer nucleating agent, passing gaseous propylene, and performing propylene slurry prepolymerization; after the prepolymerization, separating the solvent, and then passing liquid propylene and hydrogen for bulk polymerization to obtain in-situ nucleated polypropylene. After the polymer nucleating agent is prepared in one step, gaseous propylene is directly passed for slurry prepolymerization, so that the catalyst particles are fully broken to release the active center to the maximum extent to improve the catalytic activity of the catalyst in the bulk polymerization of propylene, and the finally prepared in-situ nucleated polypropylene containing a low concentration of polymer nucleating agent exhibits a higher crystallization temperature and crystallinity. The experimental results show that the crystallization temperature of the in-situ nucleated polypropylene is higher than 128°C, and the crystallinity is greater than 55%; the concentration of the polymer nucleating agent in the in-situ nucleated polypropylene is 20-30ppm.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing in-situ nucleated polypropylene, comprising the following steps: 1) Add 10 mg of titanium-containing main catalyst, 1 ml of co-catalyst triethylaluminum, 0.05 mol / L of concentration, and 15 mg of nucleating agent monomer vinyl cyclohexane into a reactor, and then add 100 mL of solvent n-hexane to react to obtain a catalyst loaded with a polymer nucleating agent; the reaction temperature of step 1) is 30° C., and the reaction time is 15 hours; the titanium-containing main catalyst is a spherical CS series catalyst of titanium tetrachloride loaded with magnesium chloride, and the titanium content is 2.3 wt%; 2) Mix 1 mL of triethylaluminum as a co-catalyst, 0.5 mL of cyclohexylmethyldimethoxysilane as an external electron donor and a catalyst loaded with a polymer nucleating agent, and introduce gaseous propylene to perform propylene slurry prepolymerization; the prepolymerization temperature in step 2) is 30° C., and the prepolymerization time is 10 min; the pressure of gaseous propylene in step 2) is 0.4 MPa; 3) After the prepolymerization, the solvent is separated, and then liquid propylene and hydrogen are introduced for bulk polymerization to obtain in-situ nucleated polypropylene; the hydrogen partial pressure is 1.5 bar; The temperature of the bulk polymerization in step 3) is 80° C., and the time of the bulk polymerization is 2 h.

2. An in-situ nucleated polypropylene, characterized in that: Prepared by the preparation method according to claim 1; The in-situ nucleated polypropylene has a crystallization temperature higher than 128°C and a crystallinity higher than 55%; The concentration of the polymer nucleating agent in the in-situ nucleated polypropylene is 20-30 ppm.

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