Polyolefin polymer, polymerization system and polymerization method of polyolefin

Abstract

The invention relates to a polyolefin polymer and a polymerization system and a polymerization method for preparing the polyolefin polymer, the polyolefin polymer comprises a core part and a shell part, the density of the core part is 0.857-0.910 g / cm < 3 >, the density of the shell part is 0.890-0.940 g / cm < 3 >, and the density of the shell part is higher than that of the core part.

Description

Technical Field

[0001] The present invention relates to a polyolefin polymer, a polyolefin polymerization system and a polymerization method. Background Art

[0002] A method for producing linear low-density polyethylene (LLDPE) by a gas phase process using a fluidized bed reactor is widely known. Specifically, ethylene monomer and a comonomer are copolymerized in the presence of a catalyst.

[0003] Among them, in the case of preparing polymers such as linear low-density polyethylene, a comonomer with more than 4 carbon atoms compared to the ethylene monomer is used. Due to the low vapor pressure of the comonomer, it condenses in the polymerization reactor and is absorbed by the polymer, causing the polymer to swell. The polymer containing a large amount of comonomer has low crystallinity and low melting point, and becomes a sticky wet resin in the polymerization reactor. Since this sticky polymer has a sticky characteristic in the reactor, fluidization is hindered, which has an adverse effect on the continuous operation of the gas phase polymerization reactor.

[0004] U.S. Patent Publication No. 4,994,534 describes a process for preparing viscous polymers such as ethylene / propylene rubber by adding silica or clay during the polymerization process. Adding these materials to the reactor not only produces polymers that are unusable in many applications, but may also become a cause of contamination of heat exchangers, compressors and other reactor systems.

[0005] Similarly, U.S. Patent No. 4970279 and International Patent No. WO88 / 02379 describe methods of adding crushed inorganic materials such as silica or alumina to a reactor. In addition, U.S. Patent Nos. 5100979 and 5106926 describe processes for preparing ethylene / 1-octene copolymers using a specific titanium-based catalyst system or a specific vanadium-based catalyst system that is not used commercially. In addition, U.S. Patent No. 5017665 describes a method for preparing ethylene / 1-butene / 1-4, hexadiene under a metallocene / aluminoxane catalyst system to prepare polymers with extremely low molecular weight and low density. In addition, U.S. Patent No. 5712353 describes a method for preparing a higher molecular weight and low density elastomer using a metallocene catalyst. Such a method prepares an elastomer with a high molecular weight and low density at a temperature above 50°C. Due to the low melting point and viscous nature of the elastomer, when prepared at high temperatures, there is a high possibility of causing process problems that make continuous operation difficult.

[0006] Prior art literature

[0007] Patent Literature

[0008] (Patent Document 1) 1. U.S. Patent Publication 4994534

[0009] (Patent Document 2) 2. U.S. Patent Publication 4970279

[0010] (Patent Document 3) 3. International Publication Patent WO88 / 02379

[0011] (Patent Document 4) 4. U.S. Patent Publication 5100979

[0012] (Patent Document 5) 5. U.S. Patent Publication 5106926

[0013] (Patent Document 6) 6. U.S. Patent Publication 5017665

[0014] (Patent Document 7) 7. U.S. Patent Publication 5712353 Summary of the invention

[0015] Technical issues

[0016] The present invention provides a low-density polyolefin polymer and a polymerization system and a polymerization method thereof, which include a core part and a shell part, and have a density distribution in which the density of the shell part is greater than the density of the core part, thereby preventing the problem of difficulty in continuous operation due to viscosity and resulting in reduced process stability when the polymer surface has a low density.

[0017] Technical Solution

[0018] One embodiment of the present invention provides a polyolefin polymer, which includes a core portion and a shell portion, wherein the density of the core portion is 0.857 to 0.910 g / cm 3 The density of the shell is 0.890 to 0.940 g / cm 3 , and the density of the shell portion is higher than the density of the core portion.

[0019] The polyolefin polymer may have any one or more of the following properties (a) to (h):

[0020] (a) melt flow index (MIE (load 2.16 kg, 190° C.) of 0.1 g / 10 min to 5.0 g / 10 min;

[0021] (b) 0.870~0.900g / cm 3 density;

[0022] (c) Two or more melting temperatures (T m );

[0023] (d) having a first melting temperature (T m1 ) and the second melting temperature (Tm2 ), the difference between the first melting temperature and the second melting temperature is 30 to 70° C.;

[0024] (e) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), wherein the first melting temperature is 45 to 85°C, and the second melting temperature is 80 to 125°C;

[0025] (f) Two or more crystallization temperatures (T c );

[0026] (g) having a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), the first crystallization temperature is 40 to 100° C., and the second crystallization temperature is 70 to 110° C.;

[0027] (h) In a temperature rising elution fractionation (TREF) chromatogram, two or more peaks are shown at a temperature above 35°C, and the percentage value of the pattern area above 60°C divided by the total pattern area is 5% or more.

[0028] The core density may be 0.857 to 0.910 g / cm 3 The melting temperature can be 45 to 85°C; the shell melt flow index (MIE (load 2.16 kg, 190°C)) can be 0.01 g / 10min to 5.0 g / 10min, and the density can be 0.890 to 0.940 g / cm 3 The melting temperature can be 80-125°C, and in the temperature rising elution fractionation (TREF) chromatogram, a peak can be shown at a temperature above 60°C; the weight ratio of the core portion to the shell portion can be 40:60-90:10.

[0029] Another embodiment of the present invention provides a polyolefin polymerization system, which includes: one or more slurry polymerization reactors, which carry out slurry polymerization reaction on the supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; and one or more gas phase polymerization reactors, which receive the slurry reaction product, or the slurry reaction product and the feed stream, carry out gas phase polymerization reaction, and generate a gas phase reaction product containing a final polymer. Wherein, the feed stream contains monomers and comonomers, and the final polymer includes a core part and a shell part with a higher density than the core part, so as to have more than two density distributions, and the operating temperature of the slurry polymerization reactor is 20 to 70°C, which is higher than the operating temperature of the gas phase polymerization reactor.

[0030] The polyolefin polymerization system may include: a first slurry polymerization reactor, which performs a slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; and a first gas phase polymerization reactor, which receives the slurry reaction product, or the slurry reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a gas phase reaction product containing a final polymer.

[0031] The polyolefin polymerization system may include: a first slurry polymerization reactor, which performs a slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a first slurry reaction product containing a prepolymer; a second slurry polymerization reactor, which receives the first slurry reaction product from the first slurry polymerization reactor, or the first slurry reaction product and the feed stream, performs a slurry polymerization reaction, and generates a second slurry reaction product containing a prepolymer; a first gas phase polymerization reactor, which receives the second slurry reaction product from the second slurry polymerization reactor, or the second slurry reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a first gas phase reaction product containing a final polymer; and a second gas phase polymerization reactor, which receives the first gas phase reaction product from the first gas phase polymerization reactor, or the first gas phase reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a second gas phase reaction product containing a final polymer.

[0032] The catalyst may be a metallocene single catalyst.

[0033] The monomer may be ethylene.

[0034] The comonomer may be any one or more selected from the group consisting of 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene, and 1-octene.

[0035] The operating temperature of the slurry polymerization reactor may be 40-60°C, and the operating temperature of the gas phase polymerization reactor may be 30-50°C.

[0036] The gas phase polymerization reactor can be operated at a MIT lower than that determined according to ASTM 3417-83. 15 The temperature of the melt was 0.1°C (15 wt% melting initiation temperature).

[0037] The second gas phase polymerization reactor may be operated in a high sorption mode. In the high sorption mode, the adsorbent may be used in an amount of 0.1 to 30 parts by weight relative to 100 parts by weight of the total circulating gas flow.

[0038] Another embodiment of the present invention provides a method for polymerizing polyolefins, the method comprising: a slurry polymerization step, in the presence of a catalyst, subjecting a feed composition containing monomers and comonomers to a slurry polymerization reaction one or more times to generate a slurry reaction product containing a prepolymer; and a gas phase polymerization step, subjecting the slurry reaction product obtained above, or the slurry reaction product and the feed composition to a gas phase polymerization reaction one or more times to generate a gas phase reaction product containing a final polymer. The reaction temperature of the slurry polymerization step is 20 to 70° C., and is carried out at a temperature higher than the reaction temperature of the gas phase polymerization step, and the final polymer includes a core portion and a shell portion having a higher density than the core portion, thereby having two or more density distributions.

[0039] The polymerization method of the polyolefin may include: a slurry polymerization step, in which a feed composition containing monomers and comonomers is subjected to a slurry polymerization reaction in the presence of the catalyst to generate a slurry reaction product containing a prepolymer; and a gas phase polymerization step, in which the slurry reaction product obtained above, or the slurry reaction product and the feed composition are subjected to a gas phase polymerization reaction to generate a final polymer.

[0040] The polymerization method of polyolefin may include: a first slurry polymerization step, in the presence of a catalyst, subjecting a feed composition containing monomers and comonomers to a primary slurry polymerization reaction to generate a first slurry reaction product containing a prepolymer; a second slurry polymerization step, subjecting the first slurry reaction product obtained above, or the first slurry reaction product and the feed composition to a secondary slurry polymerization reaction to generate a second slurry reaction product containing a prepolymer; a first gas phase polymerization step, subjecting the second slurry reaction product obtained above, or the second slurry reaction product obtained above, and the feed composition to a primary gas phase polymerization reaction to generate a first gas phase reaction product containing a final polymer; and a second gas phase polymerization step, subjecting the first gas phase reaction product obtained above, or the first gas phase reaction product and the feed composition to a secondary gas phase polymerization reaction to generate a second gas phase reaction product containing a final polymer.

[0041] The slurry polymerization reaction can generate a prepolymer having a hollow structure and form the shell of the final polymer, and the gas phase polymerization reaction can fill the hollow of the prepolymer with a product having a lower density than the prepolymer and form the core of the final polymer.

[0042] The second slurry polymerization step can form a slurry having a density of 0.890 to 0.940 g / cm 3 The shell portion is formed by the first gas phase polymerization step to have a density of 0.887 to 0.898 g / cm 3The core part is formed by the second gas phase polymerization step to have a density of 0.857 to 0.886 g / cm 3 of the core.

[0043] The amount of the prepolymer produced may be 10 to 60% by weight relative to the total amount of the final polymer produced.

[0044] In the slurry polymerization step, the molar ratio of the comonomer may be 0.01 to 0.3 relative to the total amount of the monomer and the comonomer.

[0045] In the gas phase polymerization step, the molar ratio of the comonomer may be 0.01 to 0.2 relative to the total amount of the monomer and the comonomer.

[0046] Beneficial Effects

[0047] By utilizing one or more slurry polymerization reactors and one or more gas phase polymerization reactors of the present invention and controlling the operating conditions of the slurry polymerization reactors and the gas phase polymerization reactors, the process stability in the preparation of polyolefin polymers can be ensured. The polyolefin polymers thus prepared include a core portion and a shell portion, and have a structure with a density distribution in which the density of the shell portion is higher than the density of the core portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1a is a flow chart showing a method for polymerizing polyolefin according to one embodiment.

[0049] Figure 1b is a flow chart showing a method for polymerizing polyolefin according to one embodiment.

[0050] Figure 1c is a flow chart showing a method for polymerizing polyolefin according to one embodiment.

[0051] Figure 2a This is a cross-sectional SEM image of the prepolymer prepared in Example 2.

[0052] Figure 2b This is a cross-sectional SEM image of the final polymer prepared in Example 2.

[0053] Figure 2c The cross-sectional SEM images of the final polymer prepared in Example 2 before and after dissolution in xylene.

[0054] Figure 3 For the final polymers prepared in Example 5 and Comparative Example 3, temperature rising elution fractionation (TREF) chromatograms showing the TREF values ​​as a function of temperature were measured.

[0055] Description of Reference Numerals

[0056] 100: Slurry polymerization

[0057] 110: First slurry polymerization reaction

[0058] 120: Second slurry polymerization reaction

[0059] 200: Gas Phase Polymerization

[0060] 210: First gas phase polymerization reaction

[0061] 220: Second gas phase polymerization reaction DETAILED DESCRIPTION

[0062] The terms or words used in the specification and claims should not be interpreted limited to the usual or dictionary meanings, but should be based on the principle that the inventor can appropriately define the concept of terms in order to best explain his invention, and should be interpreted as meanings and concepts that are consistent with the technical ideas of the present invention.

[0063] In the present invention, the term "stream" may refer to the flow of a fluid in a process, or may refer to the fluid itself flowing in a pipeline. Specifically, the "stream" may refer to both the fluid itself flowing in a pipeline connecting various devices and the flow of the fluid. In addition, the fluid may refer to a gas or a liquid, and it is not excluded that the fluid contains solid components.

[0064] Hereinafter, the embodiments are described in detail so that a person having ordinary knowledge in the technical field can easily implement them. However, the embodiments can be implemented in many different forms and are not limited to the embodiments described here.

[0065] The polyolefin polymer according to one embodiment may include a core portion and a shell portion, and the density of the core portion is 0.857 to 0.910 g / cm 3 The density of the shell is 0.890 to 0.940 g / cm 3 , and the density of the shell portion is higher than the density of the core portion.

[0066] As a polyolefin polymer with a core-shell structure having a core portion as described above and a shell portion wrapping the core portion, the core portion and the shell portion have the above-mentioned density range, and the shell portion of the polyolefin polymer, that is, the surface of the polymer has a higher density. Therefore, when preparing a low-density polymer, it is prevented that the surface density of the polymer in the polymerization step is low and the viscosity hinders the fluidization in the gas phase polymerization reactor, the polymers agglomerate, or the supporting facilities such as pipelines and heat exchangers are easily blocked, so that the preparation can be carried out through stable continuous operation.

[0067] In one embodiment, the polyolefin polymer may have any one or more of the following physical properties (a) to (h). For example, the polyolefin polymer may have any two or more or all of the following physical properties (a) to (h).

[0068] (a) melt flow index (MIE (load 2.16 kg, 190° C.) of 0.1 g / 10 min to 5.0 g / 10 min;

[0069] (b) 0.870~0.900g / cm 3 density;

[0070] (c) Two or more melting temperatures (T m );

[0071] (d) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), the difference between the first melting temperature and the second melting temperature is 30 to 70° C.;

[0072] (e) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), wherein the first melting temperature is 45 to 85°C, and the second melting temperature is 80 to 125°C;

[0073] (f) Two or more crystallization temperatures (T c );

[0074] (g) having a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), the first crystallization temperature is 40 to 100° C., and the second crystallization temperature is 70 to 110° C.;

[0075] (h) In the temperature rising elution fractionation (TREF) chromatogram, two or more peaks are shown at temperatures above 35°C, and the percentage value of the pattern area above 60°C divided by the total pattern area is 5% or more.

[0076] In (a), the melt flow index (MIE (load 2.16 kg, 190° C.)) may refer to the melt flow index value of the polyolefin polymer measured at 190° C. and load 2.16 kg according to ASTM D1238. The melt flow index of the polyolefin polymer may be, for example, 0.1 g / 10 min to 5.0 g / 10 min, 0.5 g / 10 min to 4.0 g / 10 min, or 0.6 g / 10 min to 3.2 g / 10 min. By having a melt flow index within the range, process stability and processability may be optimized.

[0077] The density in (b) may refer to the density of the polyolefin polymer measured by the density gradient method according to ASTM D1505. The density of the polyolefin polymer may be, for example, 0.870 to 0.900 g / cm 3 or 0.885~0.890g / cm 3 By having a density within the above range, a low-density polyolefin polymer can be provided.

[0078] The melting temperature in (c) may refer to the melting temperature of the polyolefin polymer measured according to ASTM 3417-83. The polyolefin polymer may have two or more melting temperature distributions. For example, the polyolefin polymer may have 2 to 4, 2 to 3 or 2 melting temperature distributions.

[0079] The polyolefin polymer in (d) may have a first melting temperature (T m1 ) and the second melting temperature (T m2 ), the difference between the first melting temperature and the second melting temperature may be 30-70°C, 31-68°C or 33-38°C.

[0080] In the (e), the first melting temperature may be 45-85°C, 50-85°C or 60-70°C, and the second melting temperature may be 80-125°C, 90-120°C or 95-110°C.

[0081] The same as the melting temperature, the crystallization temperature (T c ) may refer to the crystallization temperature of the polyolefin polymer measured according to ASTM 3417-83. The polyolefin polymer may have more than two crystallization temperatures. For example, the polyolefin polymer may have 2 to 4, 2 to 3 or 2 crystallization temperature distributions.

[0082] The polyolefin polymer in (g) may have a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), wherein the first crystallization temperature may be 40-100°C, 43-97°C or 44-50°C. In addition, the second crystallization temperature may be 70-110°C, 72-109°C or 74-87°C.

[0083] The temperature rising elution fractionation (TREF) chromatogram in (h) may be obtained by analyzing the polyolefin polymer using a cross-fractionation chromatogram (CFC, PolymerChar CFC-2) device. The temperature rising elution fractionation (TREF) chromatogram of the polyolefin polymer may show more than 2, 2 to 5, or 2 peaks at a temperature above 35°C. In the temperature rising elution fractionation (TREF) chromatogram, the percentage value of the graph area above 60°C divided by the total graph area may be 5% or more, 5 to 55%, or 5 to 50%. As described above, the presence of two or more peaks in the temperature rising elution fractionation (TREF) chromatogram can confirm that the polyolefin polymer has a density gradient, and the percentage value of the graph area above 60°C divided by the total graph area is 5% or more, which can confirm that the relatively high-density shell formed by the slurry polymerization reaction and melted out at a high temperature is well formed.

[0084] In one embodiment, the shell part can be formed by slurry polymerization in the polymerization system or polymerization method of polyolefin described below. Specifically, in the polyolefin polymer, the shell part with a hollow structure and a relatively high density can be formed first.

[0085] The density of the shell portion may be, for example, 0.890 to 0.940 g / cm 3 , 0.895~0.930g / cm 3 or 0.900~0.922g / cm 3 .

[0086] The melt flow index (MIE (load 2.16 kg, 190° C.)) of the shell portion may be, for example, 0.01 g / 10 min to 5.0 g / 10 min, 0.05 g / 10 min to 3.5 g / 10 min, or 0.05 g / 10 min to 2.0 g / 10 min.

[0087] The melting temperature of the shell portion may be, for example, 80 to 125°C, 90 to 120°C, or 95 to 110°C.

[0088] The shell portion may have one peak at a temperature of 60° C. or higher in a temperature rising elution fractionation (TREF) chromatogram.

[0089] In one embodiment, the core part may be formed by gas phase polymerization in the polyolefin polymerization system or polymerization method described below. Specifically, in the polyolefin polymer, the core part may be formed into a hollow structure of the shell part formed by the slurry polymerization reaction filled with a product of relatively low density.

[0090] The density of the core portion may be, for example, 0.857 to 0.910 g / cm 3 , 0.857~0.900g / cm 3 or 0.857~0.898g / cm 3 .

[0091] The melting temperature of the core may be, for example, 45 to 85°C, 50 to 85°C, or 60 to 70°C.

[0092] The weight ratio of the core part to the shell part can be 40:60 to 90:10, 50:50 to 80:20 or 50:50 to 70:30. By forming the core part and the shell part at a weight ratio within the range, a low-density polyolefin polymer can be provided while preventing the lower-density core part from leaking to the polymer surface, thereby further improving process stability.

[0093] As described above, the polyolefin polymer formed by a core and a shell with different physical properties not only has the characteristic of low density, but also has a higher density hollow shell forming the surface, and a lower density core filling the hollow interior of the shell, which can prevent the problem of hindering process stability due to the sticky and humid characteristics when the polymer surface density is low.

[0094] The melt flow index (MIE (load 2.16 kg, 190° C.) of the polyolefin polymer may be, for example, 0.1 g / 10 min to 5.0 g / 10 min, 0.5 g / 10 min to 4 g / 10 min, or 0.6 g / 10 min to 3.2 g / 10 min.

[0095] According to one embodiment, a polyolefin polymerization system may include: one or more slurry polymerization reactors, which carry out slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; and one or more gas phase polymerization reactors, which receive the slurry reaction product, or the slurry reaction product and the feed stream, carry out gas phase polymerization reaction, and generate a gas phase reaction product containing a final polymer. Wherein, the feed stream contains monomers and comonomers, and the final polymer includes a core part and a shell part with a higher density than the core part, so as to have more than two density distributions, and the operating temperature of the slurry polymerization reactor is 20 to 70°C, which may be higher than the operating temperature of the gas phase polymerization reactor.

[0096] The polyolefin polymerization system may be a system for preparing a final polymer, ie, the above-mentioned polyolefin polymer.

[0097] In one embodiment, the one or more slurry polymerization reactors and the one or more gas phase polymerization reactors may each be connected in series.

[0098] In one embodiment, the catalyst may use a single metallocene catalyst. The metallocene may be represented by the chemical formula LnMQp, wherein M is a metal of group IIIB, group IVB, group VB or group VIB; Q is a hydrocarbon group or halogen having 1 to 20 carbon atoms; p is the atomic valence of M -2, and L is a ligand bound to the metal M.

[0099] Compared with the existing Ziegler-Natta catalysts, this metallocene catalyst has high activity and high copolymerization reactivity, and is considered to be a catalyst system for producing polyolefins with excellent product properties. As a homogeneous catalyst, the metallocene catalyst can be loaded on a suitable carrier for use. For example, the carrier can be silicon and / or aluminum oxide, and as a specific example, it can be silicon dioxide having an OH group or other functional groups containing active hydrogen atoms, and can be in the form of porous spherical particles.

[0100] The metallocene catalyst may be supported on a carrier together with a cocatalyst, and the cocatalyst may be an alkylaluminoxane. The alkylaluminoxane may contain linear and / or cyclic alkylaluminoxane oligomers. When the alkylaluminoxane is a linear alkylaluminoxane oligomer, the alkylaluminoxane is represented by the chemical formula R-(Al(R)-O) n -AlR2 represents a cyclic alkylaluminoxane oligomer, represented by the chemical formula (-Al(R)-O-) m It means that R is C1-C8 alkyl, preferably methyl, n is 1-40, preferably 10-20, and m is 3-40, preferably 3-20. The alkylaluminoxane is a mixture of oligomers with a wide molecular weight distribution, and the average molecular weight can usually be 800-1200.

[0101] In an embodiment, the feed stream may contain monomers and comonomers.

[0102] The monomer may be ethylene.

[0103] The comonomer may be any one or more selected from the group consisting of 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene and 1-octene. As a specific example, the comonomer may be any one or more of 1-butene and 1-hexene.

[0104] The feed stream may also contain a diluent. The diluent may be any one or more of an inert gas and an alkane. The inert gas may include nitrogen, helium, neon, etc., and the alkane may include butane, propane, isobutane, isopentane, hexane, and isomers thereof. As described above, the process may include: using a diluent, contacting a catalyst with a monomer and a comonomer in a slurry polymerization reactor and a gas phase polymerization reactor to generate a polyolefin polymer.

[0105] In the presence of the catalyst, when a feed stream containing ethylene and comonomers is polymerized in a system in which one or more slurry polymerization reactors and one or more gas phase polymerization reactors are arranged in sequence, a polyolefin polymer can be prepared. As a specific example, it can be a polyolefin elastomer, and as a more specific example, it can be a low-density polyethylene.

[0106] In one embodiment, the operating temperature of the slurry polymerization reactor may be 20-70° C. or 40-60° C. In addition, the operating temperature of the gas phase polymerization reactor is lower than the operating temperature of the slurry polymerization reactor, for example, it may be 30-50° C. or 35-48° C. As described above, by lowering the operating temperature of each reactor to prepare the above-mentioned final polymer, the portion of the viscous and wet resin that hinders the fluidization of the reactor can be minimized, further improving the process stability.

[0107] In one embodiment, the operating pressure of the slurry polymerization reactor may be 5-30K / G, 10-25K / G or 20-25K / G. Furthermore, the operating pressure of the gas phase polymerization reactor may be adjusted to be lower than the operating pressure of the slurry polymerization reactor. For example, the pressure of the gas phase polymerization reactor may be operated at 10-20K / G or 10-15K / G depending on the temperature of the slurry polymerization reactor. As described above, the above-mentioned final polymer is prepared by reducing the operating pressure of each reactor, thereby minimizing the portion of the viscous and wet resin that hinders the fluidization of the reactor, and further improving the process stability. Here, the pressure unit K / G refers to kg / cm 2 .

[0108] In one embodiment, through multi-stage polymerization in one or more slurry polymerization reactors and one or more gas phase polymerization reactors, in the slurry polymerization reaction, a prepolymer having a relatively high density and forming a shell of a hollow structure is prepared, and in the gas phase polymerization reaction, a polyolefin polymer is prepared, that is, a polyolefin elastomer (POE) is filled into the hollow interior of the prepolymer particles to obtain a final polymer, wherein the final polymer can have the physical properties of a polyolefin elastomer.

[0109] In one embodiment, the molar ratio of ethylene and comonomer alpha olefin in each reactor can be adjusted to 0.01 to 0.3 according to the type of comonomer. For example, in the slurry polymerization reactor, the molar ratio of the comonomer can be 0.01 to 0.3, 0.05 to 0.3 or 0.07 to 0.27 relative to the total amount of the monomer and the comonomer, and in the gas phase polymerization reactor, the molar ratio of the comonomer can be 0.01 to 0.2 or 0.05 to 0.18 relative to the total amount of the monomer and the comonomer. By making the comonomer ratio of each reactor different, a polymer having more than two melting temperatures or more than two crystallinity temperatures and other physical properties can be prepared. By having a polymer with a high melting temperature and a low glass transition temperature (Tg), great advantages can be exerted in the processing part and the physical property part.

[0110] The prepolymer prepared in the slurry polymerization reactor may account for 10 to 60% by weight relative to the total amount of the final polymer produced. For example, the prepolymer may be 20 to 50% by weight or 30 to 50% by weight of the total amount of the final polymer. By adjusting the weight ratio of the prepolymer to the total amount of the final polymer within the above range, the overall density can be increased, and a high-density shell can be firmly formed without reducing the physical properties of the final polymer, and the polymer prepared in the gas phase polymerization reactor is almost absent from the outside, thereby improving process stability.

[0111] In one embodiment, the gas phase polymerization reactor can be operated at a MIT lower than 100 % as determined by ASTM 3417-83. 15 (15 wt% melting start temperature). Specifically, the temperature below MIT 15 The temperature is to ensure process stability, and the temperature of each reactor is operated at a lower temperature to set the process operating temperature, which is lower than MIT 15 The temperature is measured by DSC instrument according to ASTM 3417-83, at 10°C / min, from 25°C to 200°C, with the portion showing 15wt% melt area percent in the first scan as the reference.

[0112] As an example, the gas phase polymerization reactor is below MIT 15 The temperature of the gas phase polymerization reactor can be 40 to 80°C, 40 to 70°C or 40 to 65°C. 15If the temperature is too low under the same conditions, the polymer will agglomerate, which may reduce the process stability. On the other hand, if the reactor temperature is too low during operation to ensure process stability, the output will be greatly reduced. In addition, in the preparation process of polyolefin polymers with high comonomer content, when the output increases, a high local comonomer ratio will occur, which will increase the adhesion of the polymer and generate heterogeneous polymers, which will become a factor of process failure. The range below MIT 15 Such problems can be prevented by adjusting the temperature of the gas phase polymerization reactor.

[0113] In one embodiment, when the slurry polymerization reactor is arranged at the front end of the gas phase polymerization reactor, not only can the metallocene catalyst be prevented from being directly exposed to the gas phase polymerization reactor, but also the size of the polymer can be further increased by the slurry polymerization reaction, which is beneficial to process stability. In addition, when a low-density prepolymer is prepared in a slurry polymerization reactor, the polymer having the physical properties of a polyolefin elastomer on the outside increases, and the polymer has a viscous property as a whole, which may cause problems that hinder process stability.

[0114] According to one embodiment, the final polymer may be the above-mentioned polyolefin polymer. Specifically, the final polymer includes a core part and a shell part, and the density of the core part may be 0.857-0.910 g / cm 3 The density of the shell portion may be 0.890 to 0.940 g / cm 3 , the density of the shell portion may be higher than the density of the core portion.

[0115] The final polymer may have any one or more of the following physical properties (a) to (h). For example, the polyolefin polymer may have any two or more or all of the following physical properties (a) to (h).

[0116] (a) melt flow index (MIE (load 2.16 kg, 190° C.) of 0.1 g / 10 min to 5.0 g / 10 min;

[0117] (b) 0.870~0.900g / cm 3 density;

[0118] (c) Two or more melting temperatures (T m );

[0119] (d) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), the difference between the first melting temperature and the second melting temperature is 30 to 70° C.;

[0120] (e) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), wherein the first melting temperature is 45 to 85°C, and the second melting temperature is 80 to 125°C;

[0121] (f) Two or more crystallization temperatures (T c );

[0122] (g) having a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), the first crystallization temperature is 40 to 100° C., and the second crystallization temperature is 70 to 110° C.;

[0123] (h) In a temperature rising elution fractionation (TREF) chromatogram, two or more peaks are shown at a temperature above 35°C, and the percentage value of the pattern area above 60°C divided by the total pattern area is 5% or more.

[0124] In one embodiment, the shell, i.e., the prepolymer prepared in the slurry polymerization reactor, may have a density of, for example, 0.890 to 0.940 g / cm 3 , 0.895~0.930g / cm 3 or 0.900~0.922g / cm 3 .

[0125] The melt flow index (MIE (load 2.16 kg, 190° C.)) of the shell portion may be, for example, 0.01 g / 10 min to 5.0 g / 10 min, 0.05 g / 10 min to 3.5 g / 10 min, or 0.05 g / 10 min to 2.0 g / 10 min.

[0126] The melting temperature of the shell portion may be, for example, 80 to 125°C, 90 to 120°C, or 95 to 110°C.

[0127] The shell portion may have one peak at a temperature of 60° C. or higher in a temperature rising elution fractionation (TREF) chromatogram.

[0128] In one embodiment, the density of the core formed in the hollow interior of the prepolymer by the gas phase polymerization reaction may be, for example, 0.857 to 0.910 g / cm 3 , 0.857~0.900g / cm 3 or 0.857~0.898g / cm 3 .

[0129] The melting temperature of the core may be, for example, 45 to 85°C, 50 to 85°C, or 60 to 70°C.

[0130] The melt flow index (MIE (load 2.16 kg, 190° C.)) of the final polymer may be, for example, 0.1 g / 10 min to 5.0 g / 10 min, 0.5 g / 10 min to 4 g / 10 min, or 0.6 g / 10 min to 3.2 g / 10 min.

[0131] In the final polymer, the weight ratio of the core part to the shell part may be 40:60 to 90:10, 50:50 to 80:20, or 50:50 to 70:30. By forming the core part and the shell part at a weight ratio within the above range, a final polymer having the characteristics of a polyolefin elastomer at a low density can be provided while preventing the fluidization from being hindered due to the viscous or wet physical properties, thereby reducing the process stability.

[0132] As described above, the shell portion and the core portion have different physical properties from each other, so that two or more characteristics such as melting temperature and crystallization temperature appear in one polyolefin polymer.

[0133] As an example, the polyolefin polymerization system may include a primary slurry polymerization reactor and a primary gas phase polymerization reactor. In this case, the polyolefin polymerization system may include: a first slurry polymerization reactor, which performs a slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; and a first gas phase polymerization reactor, which receives the slurry reaction product, or the slurry reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a gas phase reaction product containing a final polymer.

[0134] As another example, the polyolefin polymerization system may include a primary slurry polymerization reactor and a secondary gas phase polymerization reactor. In this case, the polyolefin polymerization system may include: a first slurry polymerization reactor, which performs a slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; a first gas phase polymerization reactor, which receives the slurry reaction product from the first slurry polymerization reactor, or the slurry reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a first gas phase reaction product containing a final polymer; and a second gas phase polymerization reactor, which receives the first gas phase reaction product from the first gas phase polymerization reactor, or the first gas phase reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a second gas phase reaction product containing a final polymer.

[0135] As another example, the polyolefin polymerization system may include a two-stage slurry polymerization reactor and a two-stage gas phase polymerization reactor. In this case, the polyolefin polymerization system may include: a first slurry polymerization reactor, which performs a slurry polymerization reaction on a supplied feed stream in the presence of a catalyst to generate a first slurry reaction product containing a prepolymer; a second slurry polymerization reactor, which receives the first slurry reaction product from the first slurry polymerization reactor, or the first slurry reaction product and the feed stream, performs a slurry polymerization reaction, and generates a second slurry reaction product containing a prepolymer; a first gas phase polymerization reactor, which receives the second slurry reaction product from the second slurry polymerization reactor, or the second slurry reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a first gas phase reaction product containing a final polymer; and a second gas phase polymerization reactor, which receives the first gas phase reaction product from the first gas phase polymerization reactor, or the first gas phase reaction product and the feed stream, performs a gas phase polymerization reaction, and generates a second gas phase reaction product containing a final polymer.

[0136] In one embodiment, the first gas phase reaction product generated in the first gas phase polymerization reactor can separate unreacted gas and polymer in a filter, the separated polymer is supplied to the second gas phase polymerization reactor, and the unreacted gas can be refluxed to the first slurry polymerization reactor and / or the second slurry polymerization reactor through a purification tower.

[0137] When the temperature of the gas phase polymerization reactor is too low, the output is greatly reduced. In addition, in the preparation process of polyolefin polymers with high comonomer content, when the output increases, a high comonomer ratio may occur locally, which will increase the adhesion of the polymer and generate heterogeneous polymers, which will become a factor of process failure. The present invention adopts a method of reducing the adhesion of the polymer under high comonomer concentration conditions by using a high adsorption mode.

[0138] As a specific example, the first gas phase polymerization reactor may not be operated in a high adsorption mode, while the second gas phase polymerization reactor is operated in a high adsorption mode. The second gas phase polymerization reactor may be operated at a temperature and pressure at which the injected gas is condensed, while the gas discharged from the reactor is not condensed.

[0139] For reference, the polyolefin polymerization system may include: a circulation line extending from the upper part of the gas phase polymerization reactor and connected to the lower part of the gas phase polymerization reactor to circulate the circulating gas flow; a heat exchanger provided at the compressor provided in the circulation line and the circulation line, based on the flow direction of the circulating gas flow, provided at the rear end of the compressor. In the high adsorption mode, the amount of the adsorbent used may be 0.1 to 30 parts by weight, 2 to 20 parts by weight, or 3 to 15 parts by weight relative to 100 parts by weight of the total circulating gas flow.

[0140] When the second gas phase polymerization reactor is operated in a high adsorption mode, the adsorbent used may include propane, isobutane, isopentane, hexane and the like.

[0141] According to one embodiment, a method for polymerizing polyolefins may include: a slurry polymerization step, in the presence of a catalyst, subjecting a feed composition containing monomers and comonomers to one or more slurry polymerization reactions to generate a slurry reaction product containing a prepolymer; and a gas phase polymerization step, in which the slurry reaction product obtained above, or the slurry reaction product and the feed composition are subjected to one or more gas phase polymerization reactions to generate a gas phase reaction product containing a final polymer. The reaction temperature of the slurry polymerization step is 20 to 70° C., and is carried out at a temperature higher than the reaction temperature of the gas phase polymerization step. The final polymer includes a core portion and a shell portion having a higher density than the core portion, so that it can have two or more density distributions.

[0142] The polyolefin polymerization method may be a method for preparing a final polymer, ie, the polyolefin polymer, using the polyolefin polymerization system described above.

[0143] In one embodiment, the catalyst may use a single metallocene catalyst. The metallocene may be represented by the chemical formula LnMQp, wherein M is a metal of group IIIB, group IVB, group VB or group VIB; Q is a hydrocarbon group or halogen having 1 to 20 carbon atoms; p is the atomic valence of M -2, and L is a ligand bound to the metal M.

[0144] Compared with the existing Ziegler-Natta catalysts, this metallocene catalyst has high activity and high copolymerization reactivity, and is considered to be a catalyst system for producing polyolefins with excellent product properties. As a homogeneous catalyst, the metallocene catalyst can be loaded on a suitable carrier for use. For example, the carrier can be silicon and / or aluminum oxide, and as a specific example, it can be silicon dioxide having an OH group or other functional groups containing active hydrogen atoms, and can be in the form of porous spherical particles.

[0145] The metallocene catalyst may be supported on a carrier together with a cocatalyst, and the cocatalyst may be an alkylaluminoxane. The alkylaluminoxane may contain linear and / or cyclic alkylaluminoxane oligomers. When the alkylaluminoxane is a linear alkylaluminoxane oligomer, the alkylaluminoxane is represented by the chemical formula R-(Al(R)-O) n -AlR2 represents; in the case of a cyclic alkylaluminoxane oligomer, represented by the chemical formula (-Al(R)-O-) m It means that R is C1-C8 alkyl, preferably methyl, n is 1-40, preferably 10-20, and m is 3-40, preferably 3-20. The alkylaluminoxane is a mixture of oligomers with a wide molecular weight distribution, and the average molecular weight can usually be 800-1200.

[0146] In an embodiment, the feed stream may contain monomers and comonomers.

[0147] The monomer may be ethylene.

[0148] The comonomer may be any one or more selected from the group consisting of 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene and 1-octene. As a specific example, the comonomer may be any one or more of 1-butene and 1-hexene.

[0149] The feed stream may also contain a diluent. The diluent may be any one or more of an inert gas and an alkane. The inert gas may include nitrogen, helium, neon, etc., and the alkane may include butane, propane, isobutane, isopentane, hexane, and isomers thereof. As described above, the process may include: using a diluent, contacting the monomer and the comonomer in a slurry polymerization reactor and a gas phase polymerization reactor to generate a polyolefin polymer.

[0150] In the presence of the catalyst, when a feed stream containing ethylene and comonomers is polymerized in a system in which one or more slurry polymerization reactors and one or more gas phase polymerization reactors are arranged in sequence, a polyolefin polymer can be prepared. As a specific example, it can be a polyolefin elastomer, and as a more specific example, it can be a low-density polyethylene.

[0151] In one embodiment, the temperature of the slurry polymerization reaction may be 20-70° C. or 40-60° C. In addition, the temperature of the gas phase polymerization reaction is lower than the temperature of the slurry polymerization reaction, for example, it may be 30-50° C. or 35-48° C. As described above, by lowering the temperature of each reaction to prepare the above-mentioned final polymer, the portion of the viscous and wet resin that hinders the fluidization of the reactor can be minimized, further improving the process stability.

[0152] In one embodiment, the pressure of the slurry polymerization reaction can be 5-30K / G, 10-25K / G or 20-25K / G. In addition, the pressure of the gas phase polymerization reaction can be adjusted to a temperature below the operating pressure of the slurry polymerization reaction, for example, it can be operated at 10-20K / G or 10-15K / G according to the temperature. As described above, by reducing the operating pressure of each reactor to prepare the final polymer as described above, the part of the viscous and wet resin that hinders the fluidization of the reactor can be minimized, further improving the process stability.

[0153] In one embodiment, through multi-stage polymerization of more than one slurry polymerization reaction and more than one gas phase polymerization reaction, in the slurry polymerization reaction, a prepolymer having a relatively high density and forming a shell of a hollow structure is prepared; in the gas phase polymerization reaction, a polyolefin polymer is prepared, that is, a polyolefin elastomer (POE) is filled into the hollow interior of the prepolymer particles to obtain a final polymer, wherein the final polymer can have the physical properties of a polyolefin elastomer.

[0154] In one embodiment, the molar ratio of ethylene and comonomer alpha olefin in each reaction can be adjusted to 0.01 to 0.3 according to the type of comonomer. For example, in the slurry polymerization reaction, the molar ratio of the comonomer can be 0.01 to 0.3, 0.05 to 0.3 or 0.07 to 0.27 relative to the total amount of the monomer and the comonomer, and in the gas phase polymerization reaction, the molar ratio of the comonomer can be 0.01 to 0.2 or 0.05 to 0.18 relative to the total amount of the monomer and the comonomer. By making the comonomer ratio in each reaction different, a polymer having physical properties such as more than two melting temperatures or more than two crystallinity temperatures can be prepared. By having a polymer with a high melting temperature and a low glass transition temperature (Tg), great advantages can be exerted in the processing part and the physical property part.

[0155] The prepolymer prepared in the slurry polymerization reactor may account for 10 to 60% by weight relative to the total amount of the final polymer produced. For example, the prepolymer may be 20 to 50% by weight or 30 to 50% by weight of the total amount of the final polymer. By adjusting the weight ratio of the prepolymer to the total amount of the final polymer within the above range, the overall density can be increased, and a high-density shell can be firmly formed without reducing the physical properties of the final polymer, and the polymer prepared in the gas phase polymerization reactor is almost absent from the outside, thereby improving process stability.

[0156] In one embodiment, the gas phase polymerization reaction may be carried out at a temperature below the MIT determined according to ASTM 3417-83. 15 (15 wt% melting start temperature). Specifically, the temperature below MIT15 The temperature is to ensure process stability, control the temperature of each reaction at a lower level, and set an appropriate temperature range, which is lower than MIT 15 The temperature is measured by DSC instrument according to the method of ASTM3417-83, at a rate of 10°C / min from 25°C to 200°C, with the portion having a 15 wt% melting area percentage in the first scan as the reference.

[0157] As an example, in the gas phase polymerization reaction, the 15 The temperature can be 40-80°C, 40-70°C or 40-65°C. 15 If the gas phase polymerization reaction is controlled at the same temperature, the polymer will agglomerate, which may reduce the process stability. On the other hand, if the reactor temperature is too low during operation to ensure process stability, the output will be greatly reduced. In addition, in the preparation process of polyolefin polymers with high comonomer content, when the output increases, the local comonomer ratio will be high, which will increase the adhesion of the polymer and generate heterogeneous polymers, which will become a factor of process failure. The range below MIT 15 Such problems can be prevented by adjusting the temperature of the gas phase polymerization reaction.

[0158] In one embodiment, when the slurry polymerization reactor is arranged at the front end of the gas phase polymerization reactor, not only can the metallocene catalyst be prevented from being directly exposed to the gas phase polymerization reaction conditions, but also the size of the polymer can be further increased by the slurry polymerization reaction, which is beneficial to process stability. On the contrary, when a low-density prepolymer is prepared in a slurry polymerization reaction, the polymer having the physical properties of a polyolefin elastomer on the outside increases, and the overall polymer has a viscous characteristic, which may hinder the process stability.

[0159] In one embodiment, the slurry polymerization reaction can generate a prepolymer having a hollow structure and form the shell of the final polymer, and the gas phase polymerization reaction can fill the hollow of the prepolymer with a product having a lower density than the prepolymer and form the core of the final polymer.

[0160] The polymer may be the above-mentioned polyolefin polymer. Specifically, the slurry polymerization step may be used to form a polymer having a density of 0.890 to 0.940 g / cm 3 The shell portion can be formed into a density of 0.857 to 0.910 g / cm by the gas phase polymerization step. 3 The core of the.

[0161] The final polymer may have any one or more of the following physical properties (a) to (h). For example, the polyolefin polymer may have any two or more or all of the following physical properties (a) to (h).

[0162] (a) melt flow index (MIE (load 2.16 kg, 190° C.) of 0.1 g / 10 min to 5.0 g / 10 min;

[0163] (b) 0.870~0.900g / cm 3 density;

[0164] (c) Two or more melting temperatures (T m );

[0165] (d) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), the difference between the first melting temperature and the second melting temperature is 30 to 70° C.;

[0166] (e) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), wherein the first melting temperature is 45 to 85°C, and the second melting temperature is 80 to 125°C;

[0167] (f) Two or more crystallization temperatures (T c );

[0168] (g) having a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), the first crystallization temperature is 40 to 100° C., and the second crystallization temperature is 70 to 110° C.;

[0169] (h) In a temperature rising elution fractionation (TREF) chromatogram, two or more peaks are shown at a temperature above 35°C, and the percentage value of the pattern area above 60°C divided by the total pattern area is 5% or more.

[0170] In one embodiment, the shell, i.e., the prepolymer prepared in the slurry polymerization reactor, may have a density of, for example, 0.890 to 0.940 g / cm 3 , 0.895~0.930g / cm 3 or 0.900~0.922g / cm 3 .

[0171] The melt flow index (MIE (load 2.16 kg, 190° C.)) of the shell portion may be, for example, 0.01 g / 10 min to 5.0 g / 10 min, 0.05 g / 10 min to 3.5 g / 10 min, or 0.05 g / 10 min to 2.0 g / 10 min.

[0172] The melting temperature of the shell portion may be, for example, 80 to 125°C, 90 to 120°C, or 95 to 110°C.

[0173] The shell portion may have one peak at a temperature of 60° C. or higher in a temperature rising elution fractionation (TREF) chromatogram.

[0174] In one embodiment, the density of the core formed in the hollow interior of the prepolymer by the gas phase polymerization reaction may be, for example, 0.857 to 0.910 g / cm 3 , 0.855~0.900g / cm 3 or 0.857~0.898g / cm 3 .

[0175] The melting temperature of the core may be, for example, 45 to 85°C, 50 to 85°C, or 60 to 70°C.

[0176] The melt flow index (MIE (load 2.16 kg, 190° C.) of the final polymer can be, for example, 0.1 g / 10 min to 5.0 g / 10 min, 0.5 g / 10 min to 4 g / 10 min, or 0.6 g / 10 min to 3.2 g / 10 min. In the final polymer, the weight ratio of the core portion to the shell portion can be 40:60 to 90:10, 50:50 to 80:20, or 50:50 to 70:30. By forming the core portion and the shell portion at a weight ratio within the above range, a final polymer can be provided that has the characteristics of a polyolefin elastomer at a low density while preventing the fluidization from being hindered due to the sticky or wet physical properties, thereby preventing the process stability from being reduced.

[0177] As described above, the shell portion and the core portion have different physical properties from each other, so that two or more characteristics such as melting temperature and crystallization temperature appear in one polyolefin polymer.

[0178] As an example, the polymerization method of polyolefin includes: a slurry polymerization step, in the presence of the catalyst, subjecting a feed composition containing monomers and comonomers to a slurry polymerization reaction to generate a slurry reaction product containing a prepolymer; and a gas phase polymerization step, in which the slurry reaction product obtained above, or the slurry reaction product and the feed composition are subjected to a gas phase polymerization reaction to generate a gas phase reaction product containing a final polymer.

[0179] The following Figure 1a Flow chart showing a polymerization method of polyolefin according to one embodiment. Figure 1a The polyolefin polymerization method may sequentially perform a slurry polymerization reaction 100 and a gas phase polymerization reaction 200 .

[0180] As another example, the polymerization method of polyolefin may include: a first slurry polymerization step, in the presence of a catalyst, subjecting a feed composition containing monomers and comonomers to a slurry polymerization reaction to generate a slurry reaction product containing a prepolymer; a first gas phase polymerization step, in which the slurry reaction product obtained above, or the slurry reaction product obtained above and the feed composition are subjected to a primary gas phase polymerization reaction to generate a first gas phase reaction product containing a final polymer; and a second gas phase polymerization step, in which the first gas phase reaction product obtained above, or the first gas phase reaction product obtained above and the feed composition are subjected to a secondary gas phase polymerization reaction to generate a second gas phase reaction product containing a final polymer.

[0181] As another example, the polymerization method of the polyolefin may include: a first slurry polymerization step, in the presence of a catalyst, subjecting a feed composition containing monomers and comonomers to a primary slurry polymerization reaction to generate a first slurry reaction product containing a prepolymer; a second slurry polymerization step, in which the first slurry reaction product obtained above, or the first slurry reaction product and the feed composition are subjected to a secondary slurry polymerization reaction to generate a second slurry reaction product containing a prepolymer; a first gas phase polymerization step, in which the second slurry reaction product obtained above, or the second slurry reaction product obtained above, and the feed composition are subjected to a primary gas phase polymerization reaction to generate a first gas phase reaction product containing a final polymer; and a second gas phase polymerization step, in which the first gas phase reaction product obtained above, or the first gas phase reaction product and the feed composition are subjected to a secondary gas phase polymerization reaction to generate a second gas phase reaction product containing a final polymer.

[0182] The following Figure 1b Flow chart showing a polymerization method of polyolefin according to one embodiment. Figure 1b The polyolefin polymerization method may sequentially perform a first slurry polymerization reaction 110 , a second slurry polymerization reaction 120 , a first gas phase polymerization reaction 210 , and a second gas phase polymerization reaction 220 .

[0183] In one embodiment, the first gas phase reaction product generated in the first gas phase polymerization reaction can be filtered in a filter to separate unreacted gas and polymer, and the separated polymer can be used for a second gas phase polymerization reaction, and the unreacted gas can be reused in the first slurry polymerization reaction and / or the second slurry polymerization reaction.

[0184] The following Figure 1c Flow chart showing a polymerization method of polyolefin according to one embodiment. Figure 1c The polyolefin polymerization method can sequentially carry out a first slurry polymerization reaction 110, a second slurry polymerization reaction 120, a first gas phase polymerization reaction 210 and a second gas phase polymerization reaction 220. The first gas phase reaction product generated in the first gas phase polymerization reaction 210 is filtered in a filter to separate unreacted gas and polymer, and the separated polymer is used to carry out the second gas phase polymerization reaction 220. The unreacted gas can be reused in the first slurry polymerization reaction 110 and / or the second slurry polymerization reaction 120.

[0185] When the temperature of the gas phase polymerization reaction is too low, the yield is greatly reduced. In addition, in the preparation process of polyolefin polymers with high comonomer content, when the yield increases, a high comonomer ratio may occur locally, which will increase the adhesion of the polymer and generate heterogeneous polymers, which will become a factor of process failure. The present invention adopts a method of reducing the adhesion of the polymer under high comonomer concentration conditions by using a high adsorption mode.

[0186] As a specific example, the first gas phase polymerization reactor may not be operated in a high adsorption mode, while the second gas phase polymerization reactor is operated in a high adsorption mode. The second gas phase polymerization reactor may be operated at a temperature and pressure at which the injected gas is condensed, while the gas discharged from the reactor is not condensed.

[0187] For reference, the gas phase polymerization reaction can be carried out using the following devices: a circulation line extending from the upper part of the gas phase polymerization reactor and connected to the lower part of the gas phase polymerization reactor to circulate the circulating gas flow; a heat exchanger provided at the compressor provided in the circulation line and the circulation line, based on the flow direction of the circulating gas flow, provided at the rear end of the compressor. In the high adsorption mode, the amount of the adsorbent used can be 0.1 to 30 parts by weight, 2 to 20 parts by weight, or 3 to 15 parts by weight relative to 100 parts by weight of the total circulating gas flow.

[0188] When the second gas phase polymerization reaction is operated in a high adsorption mode, the adsorbent used may include propane, isobutane, isopentane, hexane and the like.

[0189] In the case of carrying out polyolefin polymerization by including the two slurry polymerization steps and the two gas phase polymerization steps, a polyolefin having a density of 0.890 to 0.940 g / cm 3 The shell portion can be formed into a shell having a density of 0.887 to 0.898 g / cm by the first gas phase polymerization step.3 The core part is formed by the second gas phase polymerization step to have a density of 0.857 to 0.886 g / cm 3 of the core.

[0190] The density of the slurry polymerization step can be 0.890-0.940 g / cm 3 , 0.895~0.930g / cm 3 or 0.900~0.922g / cm 3 The shell part.

[0191] The first gas phase polymerization step can form a nanostructured carbon nanotube with a density of 0.887 to 0.898 g / cm 3 or 0.888~0.897g / cm 3 The core of the.

[0192] The second gas phase polymerization step can form a carbon nanotube with a density of 0.857 to 0.886 g / cm 3 or 0.857~0.884g / cm 3 The core of the.

[0193] As described above, a shell with a relatively high density can be formed by slurry polymerization, a core with a lower density than the slurry polymerization can be formed by a first gas phase polymerization, and a core with a lower density than the first gas phase polymerization can be formed by a second gas phase polymerization, thereby preparing a polyolefin polymer. Such a density gradient difference allows the catalyst to prepare a prepolymer with a relatively high density in the slurry polymerization compared to the gas phase polymerization, and when the first and second gas phase polymerizations are subsequently performed, the process stability can be improved. The prepared polyolefin polymer can have a high melting temperature and a low melting temperature through a density gradient, that is, it has more than two melting temperatures and a low glass transition temperature. Due to the characteristics of this polyolefin polymer, the rotation rate increases during molding, the processing productivity increases, and the low glass transition temperature can improve physical properties such as rebound elasticity.

[0194] The specific embodiments of the present invention are provided below. However, the embodiments described below are only used for specific examples or explanations of the present invention, and the present invention should not be limited thereto. In addition, the contents not recorded here can be fully obtained by technical analogy by those skilled in the art, and therefore their description is omitted.

[0195] (Preparation of polyolefin polymers)

[0196] Examples 1 to 4 and Comparative Examples 1 to 2

[0197] A polyolefin polymer, specifically a linear low-density polyethylene, is prepared by using a primary slurry polymerization reactor and a primary gas phase polymerization reactor. At this time, the operating conditions of each reactor are shown in Table 1 below.

[0198] A polymerization reaction was carried out in a batch polymerization reactor by simulating slurry polymerization and gas phase polymerization conditions using a catalyst composition prepared by using a metallocene catalyst, methylaluminoxane (MAO) and a porous carrier as a basic combination.

[0199] In order to adjust the polymerization temperature, a 2 L stainless steel autoclave reactor equipped with a jacket capable of supplying external cooling water was heated from room temperature to 110° C., and then purged with nitrogen and then purged with 400 mL of isobutane.

[0200] After adjusting the temperature, 1.5 mL of 0.2 M triethylaluminum (TEAL), an antistatic agent ( 6000, a product of Innospec Co.) 2.5 mL (1.1 mmol in hexane) and 1 L of isobutane were put into the reactor.

[0201] Then, ethylene, 1-hexene (weight %, 1-hexene input amount relative to the ethylene input) and hydrogen (mg / kg C2, hydrogen input amount (mg) relative to 1 kg of ethylene input) were added, and the supported catalyst was added to the reactor. The slurry polymerization reaction was carried out according to the polymerization conditions shown in Table 1 below. During the polymerization, the ethylene partial pressure remained unchanged, and 1-hexene and hydrogen were linked and continuously added with ethylene. After the slurry polymerization was completed, the unreacted 1-hexene and isobutane were discharged.

[0202] To carry out the gas phase polymerization reaction, 100 psi of nitrogen was injected into the gas phase polymerization reactor as a diluent, 250 ppm of an antistatic agent was injected, and the temperature was adjusted to 48°C.

[0203] After adjusting the temperature, a gas phase polymerization reaction was carried out according to the polymerization conditions shown in the following Table 1. After the reaction was completed, the unreacted gas was discharged, and then the reactor was opened to obtain a linear low-density polyethylene (LLDPE) resin with free fluidity as the final polymer, and its physical properties were measured and shown.

[0204]

Table 1

[0205]

[0206]

[0207] 1) MIE in a gas phase polymerization reactor is a value measured on the final polymer.

[0208] In the above Table 1 and the following Table 2, the measuring methods of the various properties are as follows.

[0209] Melt flow index (MIE, MI2.16): measured at 190°C and 2.16 kg load according to ASTM D1238.

[0210] High load melt flow index (MIF, MI21.6): measured at 190°C and 21.6 kg load according to ASTM D1238.

[0211] Melt flow index ratio (SR, MFRR): calculated from MIF / MIE (F / E).

[0212] Density: Measured by density gradient method according to ASTM D1505.

[0213] BD: Bulk density (apparent density) is measured according to ASTM D1895.

[0214] Molecular weight and molecular weight distribution: Determined as follows using a gel permeation chromatography (GPC-RI; Polymer Laboratory Inc. 220 System) equipped with a refractive index detector (Refractive Index Detector; RI Detector). Two Olexis and one Guard were used as separation columns, and the column temperature was maintained at 160°C. Calibration was performed using a standard polystyrene kit from Polymer Laboratory Inc. Trichlorobenzene containing 0.0125 wt% antioxidant (BHT) was used as the eluent, the sample concentration was 1.0 mg / mL, and the measurement was performed for 27 minutes under the conditions of an injection volume of 0.2 mL and a pump flow rate of 1.0 mL / min. The number average molecular weight (Mn), weight average molecular weight (Mw) and Z average molecular weight (Mz) were converted to polyethylene and calculated after universal calibration using polystyrene standard substances Easical A and Easical B (products of Agilent).

[0215] Melting temperature (T m ), crystallization temperature (T c ): measured by DSC instrument according to ASTM 3417-83, at 10°C / min in the temperature range of 25 to 200°C, using the value displayed by the second scan.

[0216] Glass transition temperature (T g): measured by DSC instrument according to ASTM 3417-83, at 40°C / min in the temperature range of -80 to 200°C, using the value displayed by the second scan.

[0217] MIT 15 : Measured by DSC instrument according to ASTM 3417-83, at 10°C / min, at 25-200°C, with the portion showing 15 wt% melting area percentage in the first scan as the reference.

[0218] Comonomer (weight %): analyzed and calculated by 13C NMR according to ASTM D5017.

[0219] Temperature Rising Elution Fractionation (TREF): The following analysis was performed using a cross-fractionation chromatography (CFC; PolymerChar CFC-2) device. Two Olexis and one Guard were used as separation columns, the column temperature was maintained at 150°C, and calibration was performed using a standard polystyrene set from Polymer Laboratory Inc. Trichlorobenzene containing 0.0125 wt% antioxidant (BHT) was used as the eluent, the sample concentration was 75 mg / mL, and the pump flow rate was 1.0 mL / min. After the sample was injected, the temperature of the oven and the sample was raised to 150°C at a heating rate of 40°C / min. After maintaining at 150°C for 60 minutes, the temperature of the sample was lowered to 95°C at a cooling rate of 40°C / min. After maintaining at 95°C for 45 minutes, it was cooled again to 30°C at a cooling rate of 0.5°C / min and maintained for 30 minutes. Then, the sample temperature was raised from 35°C to 120°C, and the temperature was divided into 22 fractions at intervals of 4°C. 0.5 mL of sample was injected into each fraction, and the molten fraction was passed through a TREF column (Column) and an Olexis column to obtain the TREF value and molecular weight at the same time. The molecular weight was universally calibrated using polystyrene standard substances Easical A and Easical B (products of Agilent) and converted into polyethylene for calculation. The data was processed using the analysis program "CFC Calibration" that came with the equipment. The analysis took about 600 minutes, and an infrared spectrometer was used as a detector.

[0220] Single density: calculated by the following formula 1.

[0221] [Formula 1]

[0222]

[0223] In Formula 1, d is the density of the final polymer, d1 and m1 are the individual density and percentage (weight %) of the polymer produced in the first slurry polymerization reactor, d2 and m2 are the individual density and percentage (weight %) of the polymer produced in the second slurry polymerization reactor, d3 and m3 are the individual density and percentage (weight %) of the polymer produced in the first gas phase polymerization reactor, d4 and m4 are the individual density and percentage (weight %) of the polymer produced in the second gas phase polymerization reactor, and m1+m2+m3+m4=1.

[0224] Among them, in the case of Examples 1 to 4 and Comparative Examples 1 to 2 using a primary slurry polymerization reactor and a primary gas phase polymerization reactor, it is assumed that a first slurry polymerization reactor and a second gas phase polymerization reactor are used, and the relevant factors of the second slurry polymerization reactor and the first gas phase polymerization reactor are removed from the formula for calculation.

[0225] Examples 5 to 7 and Comparative Example 3

[0226] A catalyst composition (M-Cat') prepared by using a metallocene catalyst and methylaluminoxane (MAO) and a porous carrier as a basic combination is used to prepare polyolefin polymers, specifically linear low density polyethylene, using a two-stage slurry polymerization reactor and a two-stage gas phase polymerization reactor. At this time, the operating conditions of each reactor are shown in Table 2 below.

[0227] The fluidized beds of the first slurry polymerization reactor and the second slurry polymerization reactor are composed of polymer particles. 1-Butene, ethylene and hydrogen are mixed together in a pipeline and injected into a circulation line. The composition injected and the physical properties of the generated prepolymer are recorded in the following Table 2.

[0228] In the first gas phase polymerization reactor and the second gas phase polymerization reactor, the injection concentrations of ethylene, hydrogen and 1-butene were adjusted to maintain the composition shown in Table 2. In addition, the prepolymer was supplied at 5 to 10 wt% of the total weight of the present polymerization composition (prepolymer + ethylene + 1-butene), and in the component concentrations of the first gas phase polymerization reactor and the second gas phase polymerization reactor in Table 2, the remaining mole % excluding ethylene, hydrogen and 1-butene was diluent propane (Propane).

[0229] The concentration of all gases is measured by online gas chromatography in the circulating gas stream. After the reaction product discharged from the first gas phase polymerization reactor passes through a filter for separating unreacted gas and polymer, the polymer is transported to the second gas phase polymerization reactor, and the separated unreacted gas is injected into the first slurry polymerization reactor after passing through a purification tower. The slurry polymerization reactor and the gas phase polymerization reactor use propane as a diluent to continuously discharge the copolymer of ethylene and 1-butene generated by the catalytic reaction, so that the fluidized bed height of the gas phase polymerization reactor remains unchanged. In order to keep the operating temperature constant, a heat exchanger is used to adjust the temperature of the circulating gas to eliminate the heat generated by the polymerization reaction.

[0230] Thereafter, the reaction product was discharged from the second gas phase polymerization reactor, and the reaction product was subjected to processes such as degassing and drying to obtain a linear low density polyethylene (LLDPE) resin as a final polymer. The physical properties of the LLDPE resin were measured, as shown in Table 2.

[0231]

Table 2

[0232]

[0233]

[0234] 1) MIE in the second gas phase reactor is a value measured on the final polymer.

[0235] In the above Table 2, the comonomer refers to 1-butene, and the comonomer molar ratio refers to the molar ratio of 1-butene relative to the total amount of ethylene and 1-butene.

[0236] (Experimental example)

[0237] Experimental Example 1: Confirmation of the structure of polyolefin polymer

[0238] 1. Cross section of prepolymer

[0239] The cross section of the prepolymer contained in the reaction product generated in the slurry polymerization reactor in Example 2 was photographed using a scanning electron microscope (SEM). The photographed image is as follows: Figure 2a shown.

[0240] from Figure 2a It can be seen that a prepolymer having a hollow structure is generated through the syrup polymerization reaction and forms the shell portion of the final polymer.

[0241] 2. Cross-section of the final polymer

[0242] The cross section of the final polymer contained in the reaction product generated in the gas phase polymerization reactor in Example 2 was photographed using a scanning electron microscope. The photographed picture is as follows: Figure 2b The densities of the shell and the core are shown in the figure.

[0243] from Figure 2b It was confirmed that a core portion with a relatively low density was formed in the hollow of the prepolymer by the gas phase polymerization reaction.

[0244] 3. Cross-section of the final polymer before and after dissolution in xylene

[0245] The cross section of the final polymer contained in the reaction product generated in the gas phase polymerization reactor in Example 2 was photographed using a scanning electron microscope, and the cross section after the final polymer was dissolved in a xylene solution was photographed. The photographed figures are as follows: Figure 2c shown. Specifically, Figure 2c The left figure is a picture taken before the final polymer is dissolved in the xylene solution, and the right figure is a picture taken after the final polymer is dissolved in the xylene solution.

[0246] The xylene dissolution test described above is an experiment that can confirm that the low-density, high-MI portion is dissolved in xylene and eluted. Figure 2c As shown, when the final polymer is dissolved in xylene, it can be confirmed that only the core part with a relatively low density is dissolved, and the shell part with a density as high as 0.916 level is not dissolved and maintained. It can be determined that the final polymer according to the present invention has a core-shell structure in which a core part with a low density is formed inside and a shell part with a high density is formed outside the core part.

[0247] Experimental Example 2: TREF Confirmation of Polyolefin Polymers

[0248] For the final polymers prepared in Examples 1 to 7 and Comparative Example 3, the TREF values ​​according to the temperature were measured by the above method, and the temperature rising elution fractionation (TREF) chromatograms were derived, which can be confirmed by Tables 1 and 2. On the other hand, for the final polymers prepared in Example 5 and Comparative Example 3, the derived temperature rising elution fractionation (TREF) chromatograms can also be confirmed by the following: Figure 3 confirm.

[0249] From Table 1, Table 2 and Figure 3 It can be seen that in the case of the final polymers according to Examples 1 to 7, two peaks were shown at a temperature of 35° C. or higher, and the percentage value of the pattern area above 60° C. divided by the total pattern area was 5% or higher. In contrast, in the case of the final polymer according to Comparative Example 3, one peak was shown at a temperature of 35° C. or higher, and the percentage value of the pattern area above 60° C. divided by the total pattern area was 3%.

Claims

1. A polyolefin polymer comprising a core portion and a shell portion, wherein: The density of the core is 0.857-0.910 g / cm 3 ; The density of the shell is 0.890-0.940 g / cm 3 ; And the density of the shell is higher than the density of the core.

2. The polyolefin polymer according to claim 1, wherein the polyolefin polymer has any one or more of the following properties (a) to (h): (a) melt flow index (MIE (load 2.16 kg, 190° C.) of 0.1 g / 10 min to 5.0 g / 10 min; (b) 0.870~0.900g / cm 3 density; (c) Two or more melting temperatures (T m ); (d) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), the difference between the first melting temperature and the second melting temperature is 30 to 70° C.; (e) having a first melting temperature (T m1 ) and the second melting temperature (T m2 ), wherein the first melting temperature is 45 to 85°C, and the second melting temperature is 80 to 125°C; (f) Two or more crystallization temperatures (T c ); (g) having a first crystallization temperature (T c1 ) and the second crystallization temperature (T c2 ), the first crystallization temperature is 40 to 100° C., and the second crystallization temperature is 70 to 110° C.; (h) In a temperature rising elution fractionation (TREF) chromatogram, two or more peaks are shown at a temperature above 35°C, and the percentage value of the pattern area above 60°C divided by the total pattern area is 5% or more.

3. The polyolefin polymer according to claim 1, wherein The density of the core is 0.857-0.910 g / cm 3 , the melting temperature is 45~85℃; The melt flow index (MIE (load 2.16 kg, 190° C.)) of the shell is 0.1 g / 10 min to 5.0 g / 10 min, and the density is 0.890 to 0.940 g / cm 3 , the melting temperature is 80-125°C, and in the temperature rising elution fractionation (TREF) chromatogram, a peak is shown at a temperature above 60°C; The weight ratio of the core part to the shell part is 40:60 to 90:

10.

4. A polyolefin polymerization system, comprising: One or more slurry polymerization reactors, which carry out slurry polymerization reaction on the supplied feed stream in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; as well as one or more gas phase polymerization reactors, which receive the slurry reaction product, or the slurry reaction product and a feed stream, and carry out a gas phase polymerization reaction to generate a gas phase reaction product containing a final polymer, wherein the feed stream comprises monomers and comonomers; The final polymer comprises a core portion and a shell portion having a higher density than the core portion, thereby having more than two density distributions; The operating temperature of the slurry polymerization reactor is 20-70° C., which is higher than the operating temperature of the gas phase polymerization reactor.

5. The polyolefin polymerization system according to claim 4, comprising: a first slurry polymerization reactor for subjecting a supplied feed stream to a slurry polymerization reaction in the presence of a catalyst to generate a slurry reaction product containing a prepolymer; as well as The first gas phase polymerization reactor receives the slurry reaction product, or the slurry reaction product and a feed stream, and performs a gas phase polymerization reaction to generate a gas phase reaction product containing a final polymer.

6. The polyolefin polymerization system according to claim 4, comprising: a first slurry polymerization reactor for subjecting a supplied feed stream to a slurry polymerization reaction in the presence of a catalyst to generate a first slurry reaction product including a prepolymer; a second slurry polymerization reactor, which receives the first slurry reaction product, or the first slurry reaction product and a feed stream from the first slurry polymerization reactor, performs a slurry polymerization reaction, and generates a second slurry reaction product containing a prepolymer; A first gas phase polymerization reactor, which receives the second slurry reaction product from the second slurry polymerization reactor, or the second slurry reaction product and a feed stream, and performs a gas phase polymerization reaction to generate a first gas phase reaction product containing a final polymer; as well as The second gas phase polymerization reactor receives the first gas phase reaction product, or the first gas phase reaction product and a feed stream from the first gas phase polymerization reactor, and performs a gas phase polymerization reaction to generate a second gas phase reaction product containing a final polymer.

7. The polyolefin polymerization system according to claim 4, wherein: The catalyst is a metallocene single catalyst.

8. The polyolefin polymerization system according to claim 4, wherein: The monomer is ethylene.

9. The polyolefin polymerization system according to claim 4, wherein: The comonomer is at least one selected from the group consisting of 1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene and 1-octene.

10. The polyolefin polymerization system according to claim 4, wherein: The operating temperature of the slurry polymerization reactor is 40-60°C, and the operating temperature of the gas phase polymerization reactor is 30-50°C.

11. The polyolefin polymerization system according to claim 4, wherein: The gas phase polymerization reactor is operated at a temperature below the MIT measured according to ASTM 3417-83. 15 (15 wt% melting onset temperature).

12. The polyolefin polymerization system according to claim 6, wherein: The second gas phase polymerization reactor is operated in a high adsorption mode, In the high adsorption mode, the amount of adsorbent used is 0.1 to 30 parts by weight relative to 100 parts by weight of the total circulating gas flow.

13. A method for polymerizing polyolefins, the method comprising: a slurry polymerization step, in which a feed composition containing monomers and comonomers is subjected to one or more slurry polymerization reactions in the presence of a catalyst to produce a slurry reaction product containing a prepolymer; as well as a gas phase polymerization step of subjecting the slurry reaction product obtained above, or the slurry reaction product and a feed composition to one or more gas phase polymerization reactions to generate a gas phase reaction product containing a final polymer; Wherein, the reaction temperature of the slurry polymerization step is 20-70°C, and is carried out at a temperature higher than the reaction temperature of the gas phase polymerization step; The final polymer includes a core portion and a shell portion having a higher density than the core portion, thereby having more than two density distributions.

14. The method for polymerizing polyolefin according to claim 13, comprising: a slurry polymerization step, in the presence of the catalyst, subjecting the feed composition containing the monomer and the comonomer to a slurry polymerization reaction to generate a slurry reaction product containing a prepolymer; as well as The gas phase polymerization step is to subject the slurry reaction product obtained above to a gas phase polymerization reaction to generate a gas phase reaction product containing a final polymer.

15. The method for polymerizing polyolefin according to claim 13, comprising: a first slurry polymerization step, in which a feed composition containing monomers and comonomers is subjected to a primary slurry polymerization reaction in the presence of the catalyst to produce a first slurry reaction product containing a prepolymer; A second slurry polymerization step, which is to subject the first slurry reaction product obtained above, or the first slurry reaction product and a feed composition to a secondary slurry polymerization reaction to generate a second slurry reaction product containing a prepolymer; A first gas phase polymerization step, in which the second slurry reaction product obtained above, or the second slurry reaction product obtained above and a feed composition are subjected to a gas phase polymerization reaction to generate a first gas phase reaction product containing a final polymer; and The second gas phase polymerization step is to subject the first gas phase reaction product obtained above, or the first gas phase reaction product and a feed composition to a secondary gas phase polymerization reaction to generate a second gas phase reaction product containing a final polymer.

16. The method for polymerizing polyolefin according to claim 13, wherein: The slurry polymerization reaction generates a prepolymer having a hollow structure and forms the shell of the final polymer; The gas phase polymerization reaction fills the hollow space of the prepolymer with a product having a lower density than the prepolymer, thereby forming the core of the final polymer.

17. The method for polymerizing polyolefin according to claim 15, wherein: The second slurry polymerization step forms a slurry having a density of 0.890 to 0.940 g / cm 3 the shell portion; The first gas phase polymerization step forms a carbon nanotube with a density of 0.887 to 0.898 g / cm 3 The core portion; The second gas phase polymerization step forms a carbon nanotube with a density of 0.857 to 0.886 g / cm 3 of the core.

18. The method for polymerizing polyolefin according to claim 13, wherein: The amount of the prepolymer produced is 10 to 60% by weight relative to the total amount of the final polymer produced.

19. The method for polymerizing polyolefin according to claim 13, wherein: In the slurry polymerization step, the molar ratio of the comonomer is 0.01 to 0.3 relative to the total amount of the monomer and the comonomer.

20. The method for polymerizing polyolefin according to claim 13, wherein: In the gas phase polymerization step, the molar ratio of the comonomer is 0.01 to 0.2 relative to the total amount of the monomer and the comonomer.

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